day13, part2

had a bug in 'recording' the failed lines for Vertical.
debugged at second field in input, which was marking only 1 column as
having 1 smudge

day11/dayEleven.go

@@ -0,0 +1,109 @@
+package day11
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+)
+
+func Run() int64 {
+	fmt.Println("hello day 11")
+
+	filename := "day11/input"
+	bytes, err := os.ReadFile(filename)
+	if err != nil {
+		panic(fmt.Sprint("cannot read file ", filename))
+	}
+
+	text := strings.TrimSpace( string(bytes) )
+	starCoords := make([]StarCoord, 0)
+
+	lines := strings.Split(text, "\n")
+
+	nonEmptyRows := make(map[int]any)
+	nonEmptyCols := make(map[int]any)
+
+	for rowNum, line := range lines {
+		for colNum, symb := range line {
+			if symb == '#' {
+				starCoords = append(starCoords, StarCoord{rowNum, colNum})
+				nonEmptyCols[colNum] = struct{}{}
+				nonEmptyRows[rowNum] = struct{}{}
+			}
+		}
+	}
+
+	emptyRowsAbove := make([]int, len(lines))
+	emptyColsToTheLeft := make([]int, len(lines))
+
+	for rowNum, _ := range lines {
+		if rowNum > 0 {
+			emptyRowsAbove[rowNum] = emptyRowsAbove[rowNum-1]
+		}
+		_, isRowNonempty := nonEmptyRows[rowNum]
+		if !isRowNonempty {
+			emptyRowsAbove[rowNum] += 1
+		}
+	}
+
+	for colNum, _ := range lines[0] {
+		if colNum > 0 {
+			emptyColsToTheLeft[colNum] = emptyColsToTheLeft[colNum-1]
+		}
+		_, isColNonempty := nonEmptyCols[colNum]
+		if !isColNonempty {
+			emptyColsToTheLeft[colNum] += 1
+		}
+	}
+
+	var distanceSum int64
+	for i := 0; i < len(starCoords); i++ {
+		for j := i+1; j < len(starCoords); j++ {
+			// calc distance between stars i and j
+			starA := starCoords[i]
+			starB := starCoords[j]
+
+			maxRow := starA.Row
+			minRow := starB.Row
+
+			if maxRow < minRow {
+				maxRow, minRow = minRow, maxRow
+			}
+
+			var multiplier int64
+			multiplier = 1000000 - 1
+
+			emptyRowsBetween := int64(emptyRowsAbove[maxRow]) - int64(emptyRowsAbove[minRow])
+
+			rowDistance := int64(maxRow) - int64(minRow) + emptyRowsBetween*multiplier
+
+			maxCol := starA.Col
+			minCol := starB.Col
+			if maxCol < minCol {
+				maxCol, minCol = minCol, maxCol
+			}
+
+			emptyColsBetween := int64(emptyColsToTheLeft[maxCol]) - int64(emptyColsToTheLeft[minCol])
+
+			colDistance := int64(maxCol) - int64(minCol) + emptyColsBetween*multiplier
+
+			distance := rowDistance + colDistance
+			log.Printf("between stars %d %+v and %d %+v distance is %d. emptyColsBetween %d ; emptyRowsBetween %d\n", i, j, starA, starB, distance, emptyColsBetween, emptyRowsBetween)
+			distanceSum += int64(distance)
+		}
+	}
+
+	// oh, i have list of all stars, i can just iterate over them and
+	// only keep rowNums for which there are stars. yeah
+
+	fmt.Println(starCoords)
+	fmt.Println(emptyRowsAbove)
+	fmt.Println(emptyColsToTheLeft)
+
+	return distanceSum
+}
+
+type StarCoord struct {
+	Row, Col int
+}

day11/example

@@ -0,0 +1,10 @@
+...#......
+.......#..
+#.........
+..........
+......#...
+.#........
+.........#
+..........
+.......#..
+#...#.....

day11/input

@@ -0,0 +1,140 @@
+........................#...............................................#................................#................................#.
+....#..............#......................#............#....................................................................#...............
+................................#.............................................................#.............................................
+.........#.....................................#...................#........................................................................
+....................................................#.......................#..............................#................................
+..#................................................................................................#................#......................#
+.........................................................#.........................#.....#..................................................
+..................................#.............................#...............................................#.............#.............
+.......#.....#...........................#..............................................................#.............................#.....
+......................#...............................#................................................................#....................
+............................#.................#........................#.....................................#..............................
+....#.................................#...............................................#.....................................................
+...............#...........................................................#............................................................#...
+..................................#...........................................................#...................#...........#.............
+....................................................................................................................................#.......
+................................................................#................#..........................#...............................
+...#..............#........#.........#.............#........................................................................................
+.........................................................#.............#.............#..............#...................#...................
+........#...................................................................................................................................
+..............................................................................................#.................................#........#..
+....................#.......................................#.....................................................#.........................
+#..............................#.......#......#...................................#......#..................................................
+...........#.......................................#......................................................................#.................
+.......................................................................................................................................#....
+............................................................................................................................................
+.........................#...................................#...............................#..............................................
+..................................#.......................................................................#.............#...................
+.........................................#...........................#...............................#.........#..........................#.
+............#......#............................................#...............................#...................................#.......
+.............................#.....................................................#........................................................
+....#........................................#...............................#.................................................#............
+......................#............................#.....#.........#........................................................................
+.........................................................................................................#..................................
+.......#........................#................................................#..........................................................
+...............................................#..........................#................#..........................................#.....
+.#................#.............................................................................................#......#....................
+..............................................................................................................................#.............
+..........................#........................#.............................................#..........................................
+.............#..........................#............................................#..............................#.......................
+........#..............................................#.....................#..........................#..................#................
+............................................................#.....#..................................................................#......
+....................#.........................#..........................#..................#...................#...........................
+..............................#...................................................#................#........................................
+.........................................#..............................................#..................................................#
+.#........#.........................................#.....................................................#.....................#...........
+.........................................................#.........................................................#........................
+......#...........................#.........................................................................................................
+................................................#........................................................................................#..
+...................................................................#...............#........................................................
+.....................#................................#..............................................................................#......
+...........#................................................................................#.....#.........................................
+....#........................#............................................#..............................................#..................
+................#.......#........................................................#........................................................#.
+#...................................................................................................................#.......................
+....................#...................#..............#.................................#...................#..............................
+.............#....................#.................................................#..................#...................#................
+.................................................................................................................#.....................#....
+................................................................................#...........................................................
+.......................#.............#....................#.................................................................................
+.......#.............................................................................................#..............#.......................
+...................#.....................................................................................................................#..
+......................................................#..................#.......................................................#..........
+..........................#..................................................................#..............................................
+............#.................................#.........................................#...................#............#..................
+.....................#......................................#......................................................#..........#.............
+.#.........................................................................#......#...................#.....................................
+............................................................................................................................................
+................................#...........................................................#...............................................
+........................................#..........................#..................................................#.................#...
+....#........................................#.....................................................#.............................#..........
+..........................................................#.................................................................................
+...............#............................................................................................................................
+..........#............#............................#.............................#...........................................#......#......
+....................................#........................................................#...............#..............................
+...........................................#..............................#...............................................................#.
+.#...........................#.......................................................................#......................................
+.........................................................#...........#....................................#.................................
+......#.......#...................#...........................#.......................#.........#..................#........................
+............................................................................#.........................................................#.....
+.....................#.........................................................................................#........#...................
+..........................#.............................................#................#........................................#.........
+............................................................................................................................................
+....#.....#.....#..................................#.........#.....................#....................#...................................
+........................................#.....................................................................................#.............
+...............................................................................................#............................................
+.......#........................#...........................................#............................................................#..
+....................#......#....................#...........................................................................................
+.........................................................#...........#..........#.............................#...........#.................
+......................................................................................#.....................................................
+....................................................................................................#................#..........#.....#.....
+............#.........#.....................#...............#..............................................#................................
+.......#............................#.......................................................................................................
+.......................................................................#......................#................#...................#........
+............................................................................................................................................
+........................................................................................................................#...................
+..........#..........#.......................#.........................................................................................#....
+...................................................................#.................#...........#..........................................
+........................................#................#..................................................................................
+................#....................................................................................................#......................
+............................................................................................................................................
+.......#....................#.................................................................#...............#.........................#...
+.................................#...........#.....#...........................................................................#............
+...........#.......................................................#....................#...................................................
+........................................#...............................................................................#...................
+............................................................................................................................................
+.....................................................................................................#......................................
+................#.........................................#..................#................................................#.......#.....
+....#................................#.............#...................................#.....................#.......#......................
+.........................#......................................#...........................................................................
+...........................................................................................#.......#........................................
+..........#.....................#..............#........................#...................................................................
+..#.........................................................................................................................................
+....................#.....................................#.......................#.........................................................
+..........................#.............#...............................................................................#.........#.........
+......................................................................................#.....................................................
+.....................................................................#..........................#...........................................
+.......#.........#...........................................................#.......................#........#............#............#...
+........................#....................................#..............................................................................
+.......................................#............................................#....................#.........................#........
+..............................................#....................................................................#........................
+..............#..................#.....................................#..........................#.........................................
+..........................................#..........#..........................#...........................................................
+.....#......................................................................................#................#..............................
+.....................#................................................................#.......................................#.............
+.....................................................................#......................................................................
+...........#.....#............................#.....................................................................................#.......
+................................#.....#..........................#........#..........................................#....................#.
+...........................#.................................................................#........#.......#.............................
+#...........................................................................................................................................
+........#........................................#...................................#......................................................
+.............................................................................................................................#..............
+.................................#..............................#........................#.........#........#...............................
+............#.....#..........................#.......................#....................................................................#.
+........................#........................................................#..........................................................
+............................................................#..............#......................................#.........................
+...#........................................................................................#...............................................
+...........................................................................................................#......................#.........
+..........#.......................................................................................#.........................................
+......................#................#............................................#.................................................#.....
+...........................#.....................#........#...................................................#.............................

day12/dayTwelve.go

@@ -0,0 +1,184 @@
+package day12
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+)
+
+func Run() int {
+	fmt.Println("hello day 12.")
+
+	start := time.Now()
+
+	filename := "day12/input"
+	bytes, err := os.ReadFile(filename)
+	if err != nil {
+		panic(fmt.Sprintf("error reading file %s\n", filename))
+	}
+
+	result := 0
+	text := string(bytes)
+	text = strings.TrimSpace(text)
+
+	// testMask, testBlocks := ReadLine(".??..??...?##. 1,1,3")
+	// blocksSum := 0
+	// for _, block := range testBlocks {
+	// 	blocksSum += block
+	// }
+	// testVariants := generatePermutations("", len(testMask), testBlocks, blocksSum, testMask)
+	// fmt.Printf("for mask %s and blocks %+v\n", testMask, testBlocks)
+	// for _, variant := range testVariants {
+	// 	fmt.Println(variant)
+	// }
+
+	var wg sync.WaitGroup
+	lines := strings.Split(text, "\n")
+	wg.Add(len(lines))
+
+	matches := make(chan int)
+	go func() {
+		wg.Wait()
+		close(matches)
+	}()
+
+	for i, line := range lines {
+		go func(line string, lineNum int){
+			mask, blockLengs := ReadLine(line)
+
+			blockLengthSum := 0
+			for _, blockLen := range blockLengs {
+				blockLengthSum += blockLen
+			}
+
+			memo := make(map[string]int)
+			variantsCount := generatePermutations("", len(mask), blockLengs, blockLengthSum, mask, memo)
+
+			log.Printf("%d : for line %s blocks %+v matches %d\n", lineNum, mask, blockLengs, variantsCount)
+			matches <- variantsCount
+			wg.Done()
+		}(line, i)
+	}
+
+	num := 0
+	for match := range matches {
+		num += 1
+		result += match
+		log.Printf("%d. intermediate: %d\n", num, result)
+		fmt.Printf("%d\n", result)
+	}
+
+	end := time.Now()
+
+	diff := end.Sub(start)
+	log.Printf("> calculated for %s", diff.String())
+
+	return result
+}
+
+func myRepeat(line, sep string, amount int) string {
+	acc := ""
+	for i := 0; i < amount; i++ {
+		acc += sep
+		acc += line
+	}
+	acc, _ = strings.CutPrefix(acc, sep)
+
+	return acc
+}
+
+// ???.### 1,1,3
+func ReadLine(line string) (string, []int) {
+	firstSplit := strings.Split(line, " ")
+	if len(firstSplit) != 2 {
+		panic(fmt.Sprintf("error splitting %s into 2", line))
+	}
+	mask := firstSplit[0]
+	mask = myRepeat(mask, "?", 5)
+	blocks := firstSplit[1]
+	blocks = myRepeat(blocks, ",", 5)
+	// log.Printf(">> repeating blocks %s", blocks)
+	blockLengthStrings := strings.Split(blocks, ",")
+	blockLengs := make([]int, len(blockLengthStrings))
+
+	for i, blockLenStr := range blockLengthStrings {
+		num, err := strconv.Atoi(blockLenStr)
+		if err != nil {
+			panic(fmt.Sprintf("error extracting num %s from %s\n", blockLenStr, line))
+		}
+		blockLengs[i] = num
+	}
+
+	return mask, blockLengs
+}
+
+func generatePermutations(curString string, targetLength int, blockLengths []int, blockLengthsSum int, mask string, memo map[string]int) int {
+
+	memoKey := fmt.Sprintf("%+v|%d", blockLengths, len(curString))
+	memoized, memoFound := memo[memoKey]
+	if memoFound {
+		return memoized
+	}
+
+	// fmt.Printf("> entering with \n%s\nfor map \n%s\n\n", curString, mask)
+	// time.Sleep(time.Second)
+	if !isVariantMatchesMask(curString, mask) {
+		return 0
+	}
+
+	// log.Printf("> entering with %s\n", curString)
+	if len(blockLengths) == 0 {
+		if len(curString) > targetLength {
+			return 0
+		}
+		variant := curString + strings.Repeat(".", targetLength-len(curString))
+		if !isVariantMatchesMask(variant, mask) {
+			return 0
+		}
+		memo[memoKey] = 1
+		return 1
+	}
+
+	nextBlock := blockLengths[0]
+	restBlocks := blockLengths[1:]
+
+	if len(curString) + blockLengthsSum + len(blockLengths) - 1 > targetLength {
+		return 0
+	}
+
+	isLast := len(restBlocks) == 0
+	rightPointRepeat := 1
+	if isLast {
+		rightPointRepeat = 0
+	}
+
+	whenPass := curString + "."
+	whenAdd := curString + strings.Repeat("#", nextBlock) + strings.Repeat(".", rightPointRepeat)
+
+	passCount := generatePermutations(whenPass, targetLength, blockLengths, blockLengthsSum, mask, memo)
+	addCount := generatePermutations(whenAdd, targetLength, restBlocks, blockLengthsSum-nextBlock, mask, memo)
+
+	memo[memoKey] = passCount + addCount
+	return passCount + addCount
+}
+
+func isVariantMatchesMask(variant, mask string) bool {
+	if len(mask) < len(variant) {
+		log.Printf("mask %s is less than variant %s\n", mask, variant)
+	}
+	maskRunes := []rune(mask)
+	for i, symb := range variant {
+		if maskRunes[i] == '?' {
+			continue
+		}
+		if maskRunes[i] != symb {
+			return false
+		}
+	}
+
+	return true
+}

day12/example

@@ -0,0 +1,6 @@
+#.#.### 1,1,3
+.#...#....###. 1,1,3
+.#.###.#.###### 1,3,1,6
+####.#...#... 4,1,1
+#....######..#####. 1,6,5
+.###.##....# 3,2,1

day12/example1

@@ -0,0 +1,6 @@
+???.### 1,1,3
+.??..??...?##. 1,1,3
+?#?#?#?#?#?#?#? 1,3,1,6
+????.#...#... 4,1,1
+????.######..#####. 1,6,5
+?###???????? 3,2,1

day12/notes.org

@@ -0,0 +1,104 @@
+#+title: Notes
+* i guess let's generate all possible? and short circuit when they are not matching mask
+how do i generate all possible?
+
+i take length of the mask, that's max size
+then for each step, either put . or put n # from the input.
+
+add to current string, and do 2 recursive calls, one with diminished 'queue', one with same
+* wrong answer on input
+it's too high
+
+and log shows:
+
+2023/12/12 15:07:52 for line ???#?.?#?#.?#???#..? blocks [4 4 5 1] matches 2
+
+and it should be 0
+** huh, nope this looks good:
+	testMask := "???#?.?#?#.?#???#..?"
+	testBlocks := []int{4,4,5,1}
+    testVariants := generatePermutations("", len(testMask), testBlocks, 14, testMask)
+	fmt.Printf("for mask %s and blocks %+v\n", testMask, testBlocks)
+	fmt.Println(testVariants)
+
+    for mask ???#?.?#?#.?#???#..? and blocks [4 4 5 1]
+[####..####..#####..# .####.####..#####..#]
+** let's check this : for line ??????#???????? blocks [7 2] matches 21
+** or this for line ?????.??#????? blocks [3 3 2 1] matches 3
+looks ok
+** this for line ??..??#?????#?##? blocks [1 1 1 1 4] matches 15
+looks good
+** for line ?#??#??#???.??.??.? blocks [1 2 3 1 1 1] matches 20
+seems ok
+** for line ???????#??.????####? blocks [1 1 1 1 1 6] matches 58
+bingo?
+
+for mask ???????#??.????####? and blocks [1 1 1 1 1 6]
+#.#.#..#.#.######...
+#.#.#..#.#..######..
+#.#.#..#.#...######.
+#.#.#..#.#....######
+#.#.#..#...#.######.
+#.#.#..#...#..######
+#.#.#..#....#.######
+#.#..#.#.#.######...
+#.#..#.#.#..######..
+#.#..#.#.#...######.
+#.#..#.#.#....######
+#.#..#.#...#.######.
+#.#..#.#...#..######
+#.#..#.#....#.######
+#.#....#.#.#.######.
+#.#....#.#.#..######
+#.#....#.#..#.######
+#..#.#.#.#.######...
+#..#.#.#.#..######..
+#..#.#.#.#...######.
+#..#.#.#.#....######
+#..#.#.#...#.######.
+#..#.#.#...#..######
+#..#.#.#....#.######
+#..#...#.#.#.######.
+#..#...#.#.#..######
+#..#...#.#..#.######
+#...#..#.#.#.######.
+#...#..#.#.#..######
+#...#..#.#..#.######
+#....#.#.#.#.######.
+#....#.#.#.#..######
+#....#.#.#..#.######
+.#.#.#.#.#.######...
+.#.#.#.#.#..######..
+.#.#.#.#.#...######.
+.#.#.#.#.#....######
+.#.#.#.#...#.######.
+.#.#.#.#...#..######
+.#.#.#.#....#.######
+.#.#...#.#.#.######.
+.#.#...#.#.#..######
+.#.#...#.#..#.######
+.#..#..#.#.#.######.
+.#..#..#.#.#..######
+.#..#..#.#..#.######
+.#...#.#.#.#.######.
+.#...#.#.#.#..######
+.#...#.#.#..#.######
+..#.#..#.#.#.######.
+..#.#..#.#.#..######
+..#.#..#.#..#.######
+..#..#.#.#.#.######.
+..#..#.#.#.#..######
+..#..#.#.#..#.######
+...#.#.#.#.#.######.
+...#.#.#.#.#..######
+...#.#.#.#..#.######
+* well, maybe overnight will calculate.
+but i guess i needed to check whether blocks are 'always' taking full width
+then i'll only need to calculate once, and then multiply
+** for example
+2023/12/12 20:40:41 699 : for line ??#?????#???.? ???#?????#???.????#?????#???.????#?????#???.????#?????#???.? blocks [3 1 2 1 3 1 2 1 3 1 2 1 3 1 2 1 3 1 2 1] matches 38294856
+
+??#?? ???#?? ?.?
+3,1,2,1 - 10+3 = 13
+
+lowest s ###.#.##.#..... - plenty of space for additional

day13/dayThirteen.go

@@ -0,0 +1,226 @@
+package day13
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+)
+
+func Run() int {
+	filename := "day13/input"
+	fmt.Println("hello day 13.", filename)
+	bytes, err := os.ReadFile(filename)
+	if err != nil {
+		panic(fmt.Sprintf("error reading file %s", filename))
+	}
+	allText := string(bytes)
+	fieldTexts := strings.Split(allText, "\n\n")
+
+	result := 0
+	for _, fieldText := range fieldTexts {
+		field := ReadField(fieldText)
+		result += Calc(field)
+	}
+
+	return result
+}
+
+func Calc(field Field) int {
+	verticals, horizontals := field.initMirrors()
+	fmt.Println(field.String())
+	fmt.Printf("field width %d and height %d\n", len(field.Symbols[0]), len(field.Symbols))
+
+	for rowNum, row := range field.Symbols {
+		for colNum, symb := range row {
+			for _, horizontalMirrorUnderCheck := range horizontals {
+				// if horizontalMirrorUnderCheck.Smaller != 4 {
+				// 	continue
+				// }
+				mirroredRow, shouldCheck := horizontalMirrorUnderCheck.reflectCoord(rowNum)
+				// log.Println("for mirror", horizontalMirrorUnderCheck.String())
+				// log.Printf("> checking row %d and mirrored %d; should %t\n", rowNum, mirroredRow, shouldCheck)
+				if shouldCheck {
+					// log.Printf("checking horizontal mirror %+v", horizontalMirrorUnderCheck)
+					// log.Printf("in should check for row %d, col %d, mirrored row %d\n", rowNum, colNum, mirroredRow)
+					mirroredSymb := field.Symbols[mirroredRow][colNum]
+					isMirrored := symb == mirroredSymb
+					if !isMirrored {
+						// log.Printf("found not mirrored : %s != %s\n", string(symb), string(mirroredSymb))
+						horizontalMirrorUnderCheck.FailedLineChecks[rowNum] += 1
+					}
+				}
+			}
+		}
+		// whole row got checked.
+		// let's mark successful line check for all that didn't fail this line check
+		for _, horizontalMirror := range horizontals {
+			_, failedCheckReported := horizontalMirror.FailedLineChecks[rowNum]
+			if !failedCheckReported {
+				horizontalMirror.SuccessfulLineChecks[rowNum] = struct{}{}
+			}
+		}
+	}
+
+	rowsAboveHorizontals := 0
+	for _, mirr := range horizontals {
+		fmt.Println("horizontal: ", mirr.String())
+		if mirr.isFullMirror() {
+			log.Printf(">> found perfect Horizontal %+v\n", mirr)
+			rowsAboveHorizontals += (mirr.Smaller + 1)
+		}
+	}
+
+	for colNum, _ := range field.Symbols[0] {
+		for rowNum, row := range field.Symbols {
+			symb := row[colNum]
+			for _, verticalMirrorUnderCheck := range verticals {
+				// if verticalMirrorUnderCheck.Smaller != 8 {
+				// 	continue
+				// }
+				mirroredCol, shouldCheck := verticalMirrorUnderCheck.reflectCoord(colNum)
+				if shouldCheck {
+					// log.Printf("checking vertical mirror %+v", verticalMirrorUnderCheck)
+					// log.Printf("in should check for row %d, col %d, mirrored col %d\n", rowNum, colNum, mirroredCol)
+					mirroredSymb := field.Symbols[rowNum][mirroredCol]
+					isMirrored := symb == mirroredSymb
+					if !isMirrored {
+						// log.Printf("found not mirrored : %s != %s\n", string(symb), string(mirroredSymb))
+						verticalMirrorUnderCheck.FailedLineChecks[colNum] += 1
+					}
+				}
+			}
+		}
+		// whole row got checked.
+		// let's mark successful line check for all that didn't fail this line check
+		for _, verticalMirror := range verticals {
+			_, failedCheckReported := verticalMirror.FailedLineChecks[colNum]
+			if !failedCheckReported {
+				verticalMirror.SuccessfulLineChecks[colNum] = struct{}{}
+			}
+		}
+	}
+	colsToLeftOfHorizontals := 0
+	for _, mirr := range verticals {
+		fmt.Println("vertical: ", mirr.String())
+		if mirr.isFullMirror() {
+			log.Printf(">> found perfect Vertical %+v\n", mirr)
+			colsToLeftOfHorizontals += (mirr.Smaller + 1)
+		}
+	}
+
+	result := colsToLeftOfHorizontals + 100*rowsAboveHorizontals
+
+	return result
+}
+
+type Field struct {
+	Symbols [][]rune
+}
+
+func ReadField(fieldText string) Field {
+	fieldText = strings.TrimSpace(fieldText)
+	lines := strings.Split(fieldText, "\n")
+
+	symbols := make([][]rune, len(lines))
+	for i, line := range lines {
+		symbols[i] = []rune(line)
+	}
+
+	return Field{
+		Symbols: symbols,
+	}
+}
+
+func (f *Field) String() string {
+	text := "\n"
+	for _, row := range f.Symbols {
+		text += string(row)
+		text += "\n"
+	}
+	return text
+}
+
+func (f *Field) initMirrors() (vertical []Mirror, horizontal []Mirror) {
+	height := len(f.Symbols)
+	width := len(f.Symbols[0])
+	amountHorizontal := height - 1
+	amountVertical := width - 1
+	horizontal = make([]Mirror, amountHorizontal)
+	vertical = make([]Mirror, amountVertical)
+
+	for rowNum := 0; rowNum < amountHorizontal; rowNum++ {
+		maxDist := min(rowNum, height - 1 - (rowNum+1))
+		// log.Println("maxDist ", maxDist, "for rowNum ", rowNum)
+		horizontal[rowNum] = Mirror{
+			Smaller:              rowNum,
+			Bigger:               rowNum + 1,
+			SuccessfulLineChecks: make(map[int]any),
+			FailedLineChecks:     make(map[int]int),
+			MaxDistToCheck:       maxDist,
+		}
+	}
+
+	for colNum := 0; colNum < amountVertical; colNum++ {
+		maxDist := min(colNum, width - 1 - (colNum+1))
+		vertical[colNum] = Mirror{
+			Smaller:              colNum,
+			Bigger:               colNum + 1,
+			SuccessfulLineChecks: make(map[int]any),
+			FailedLineChecks:     make(map[int]int),
+			MaxDistToCheck:       min(colNum, maxDist),
+		}
+	}
+
+	return
+}
+
+type Mirror struct {
+	// located between lines
+	Smaller, Bigger int
+	MaxDistToCheck  int // how many steps from mirrow have to be checked to confirm
+	// i.e if mirror between 0 and 1 - only rows 0 & 1 have to be checked, row 2 is 'mirrored' outside of the field and 'ok'
+	// value 0 means one step from 'mirror' so rows 0 and 1
+	SuccessfulLineChecks map[int]any
+	FailedLineChecks     map[int]int // from line num, to amount of errors in that line
+}
+
+func (m *Mirror)isFullMirror() bool {
+	correctFailedLinesCount := len(m.FailedLineChecks) == 2
+	if correctFailedLinesCount {
+		for failedLine, failedSymbols := range m.FailedLineChecks {
+			reflectedLine, _ := m.reflectCoord(failedLine)
+			doublyReflected, _ := m.reflectCoord(reflectedLine)
+			// log.Printf(">>>> checking failed line %d, reflected is %d; doubly %d. amount failed is %d\n", failedLine, reflectedLine, doublyReflected, failedSymbols)
+			if failedSymbols == 1 && (doublyReflected == failedLine) {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func (m *Mirror)String() string {
+	return fmt.Sprintf("Mirror (full %t) between %d and %d. successful lines: %+v ; failed lines: %+v. Max check dist: %d\n",
+		m.isFullMirror(), m.Smaller, m.Bigger, m.SuccessfulLineChecks, m.FailedLineChecks, m.MaxDistToCheck)
+}
+
+func (m *Mirror) reflectCoord(coord int) (reflected int, shouldCheck bool) {
+	dist := m.Smaller - coord
+
+	// _, distConfirmed := m.SuccessfulLineChecks[dist]
+	// if distConfirmed {
+	// 	// log.Printf("> getting dist confirmed for coord %d ; dist %d\n", coord, dist)
+	// 	return 0, false // either line already fully confirmed, or failed. no need for additional checks
+	// }
+
+	reflected = m.Bigger + dist
+	if dist < 0 {
+		dist = coord - m.Bigger
+		reflected = m.Smaller - dist
+	}
+
+	shouldCheck = dist <= m.MaxDistToCheck
+
+	return reflected, shouldCheck
+}

day13/example

@@ -0,0 +1,15 @@
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#

day13/example1

@@ -0,0 +1,7 @@
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.

day13/example2

@@ -0,0 +1,7 @@
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#

main.go

@@ -3,12 +3,12 @@ package main
 import (
 	"log"
 
-	"sunshine.industries/aoc2023/day10"
+	"sunshine.industries/aoc2023/day13"
 )
 
 func main() {
 	log.Print("> starting run:")
 
-	result := day10.Run()
+	result := day13.Run()
-	log.Printf("day10 result: %d\n****\n", result)
+	log.Printf("day13 result: %d\n****\n", result)
 }