Advent-of-Code-2023/day13/dayThirteen.go

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
}