day21: example

day21/example

@@ -0,0 +1,11 @@
+...........
+.....###.#.
+.###.##..#.
+..#.#...#..
+....#.#....
+.##..S####.
+.##..#...#.
+.......##..
+.##.#.####.
+.##..##.##.
+...........

day21/notes.org

@@ -0,0 +1,11 @@
+#+title: Notes
+* part 1
+so we aren't looking for minimal distance.
+but all plots which are end to any path of length 'steps left'
+
+so, i have to follow all possible paths to the end?
+or. length of 6 and all even - because i could be doing <- ->
+but i could be doing loop around that would increase path len by odd number
+
+let's just make direct recursive thing.
+create set of all reachable by n,

day21/stepCounter.go

@@ -0,0 +1,132 @@
+package day21
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+)
+
+func Run() int {
+	fmt.Print("hello day21")
+	filename := "day21/example"
+	field := ReadField(filename)
+	log.Print(field)
+
+	reachableBySix := field.ReachableBySteps(6, map[Coord]any{
+		Coord{Row: field.RowStart, Col: field.ColStart}: struct{}{},
+	})
+
+	fmt.Println(field.PrintCoord(reachableBySix))
+
+
+	return len(reachableBySix)
+}
+
+// let's do dijkstra?
+// i would need lots of space for edges?
+// let's use a map with minimal distances?
+// OR. just breath first traversal
+
+type Field struct {
+	RowStart, ColStart int
+	symbols            [][]rune
+}
+
+type Coord struct {
+	Row, Col int
+}
+
+
+func (f Field)ReachableBySteps(n int, startingAt map[Coord]any) map[Coord]any {
+	if n == 0 {
+		return startingAt
+	}
+	// else collect directly available
+
+	oneStepExpanded := make(map[Coord]any)
+	for cur := range startingAt {
+		for _, neighbor := range f.Neighbors(cur) {
+			oneStepExpanded[neighbor] = struct{}{}
+		}
+	}
+
+	return f.ReachableBySteps(n-1, oneStepExpanded)
+}
+
+
+func (f Field) Neighbors(c Coord) (resut []Coord) {
+	closeCoords := []Coord{
+		{Row: c.Row + 1, Col: c.Col},
+		{Row: c.Row - 1, Col: c.Col},
+		{Row: c.Row, Col: c.Col + 1},
+		{Row: c.Row, Col: c.Col - 1},
+	}
+
+	for _, close := range closeCoords {
+		symb := f.symbols[close.Row][close.Col]
+		validNextPlace := f.ValidCoord(close.Row, close.Col) &&
+			(symb == '.' || symb == 'S')
+		if validNextPlace {
+			resut = append(resut, close)
+		}
+	}
+
+	// log.Print("getting neighbors for ", c, resut)
+
+	return
+}
+
+func (f Field) ValidCoord(row, col int) bool {
+	// log.Print("check valid ", row, col, row >= 0 && row < len(f.symbols) && col >= 0 && col < len(f.symbols[0]))
+	return row >= 0 && row < len(f.symbols) && col >= 0 && col < len(f.symbols[0])
+}
+
+func (f Field) String() (result string) {
+	result += "\n"
+	for _, line := range f.symbols {
+		result += string(line)
+		result += "\n"
+	}
+
+	return
+}
+
+func ReadField(filename string) (result Field) {
+	bytes, err := os.ReadFile(filename)
+	if err != nil {
+		panic(err)
+	}
+	text := strings.TrimSpace(string(bytes))
+
+	lines := strings.Split(text, "\n")
+	rows := make([][]rune, len(lines))
+	for rowNum, line := range lines {
+		rows[rowNum] = []rune(line)
+		for colNum, symb := range line {
+			if symb == 'S' {
+				result.RowStart = rowNum
+				result.ColStart = colNum
+			}
+		}
+	}
+	result.symbols = rows
+	return
+}
+
+func (f Field)PrintCoord(coords map[Coord]any) string {
+	result := ""
+	for rowNum, row := range f.symbols {
+		for colNum, col := range row {
+			_, marked := coords[Coord{Row: rowNum, Col: colNum}]
+			if marked {
+				result += "O"
+			} else {
+				result += string(col)
+			}
+		}
+		result += "\n"
+	}
+
+	return result
+}

main.go

@@ -4,15 +4,15 @@ import (
 	"log"
 	"time"
 
-	"sunshine.industries/aoc2023/day20"
+	"sunshine.industries/aoc2023/day21"
 )
 
 func main() {
 	startTime := time.Now()
 	log.Print("> starting run:")
 
-	result := day20.Run()
-	log.Printf("\n\nday20 result: %d\n****\n", result)
+	result := day21.Run()
+	log.Printf("\n\nday21 result: %d\n****\n", result)
 	endTime := time.Now()
 	diff := endTime.Sub(startTime)
 	log.Printf("execution took %s", diff.String())