aoc2023/day-13/two.go

package main

import (
	log "github.com/sirupsen/logrus"
)

// findReflectionWithDifference returns the reflection point for an image with one smudge
func findReflectionWithDifference(image []string) (int, bool) {
	walkToEdge := func(lower, upper int) bool {
		diffs := 0
		for lower >= 0 && upper < len(image) {
			diffs += numDiffs(image[lower], image[upper])
			lower--
			upper++
		}
		return diffs == 1
	}

	for i := 0; i < len(image)-1; i++ {
		log.Debug("start point: ", image[i], " vs ", image[i+1])
		if walkToEdge(i, i+1) {
			return i, true
		}
	}
	return 0, false
}

// two returns a calculation based on reflection points for all images with one smudge
func two(lines []string) int {
	sum := 0
	for _, image := range images.img {
		log.Debug("checking for horizontal reflection")
		n, ok := horizontalReflection(image, findReflectionWithDifference)
		if ok {
			sum += 100 * (n + 1)
		}
		log.Debug("checking for vertical reflection")
		n, ok = verticalReflection(image, findReflectionWithDifference)
		if ok {
			sum += (n + 1)
		}
	}

	return sum
}