aoc2023/day-13/one.go

package main

import (
	"strings"

	log "github.com/sirupsen/logrus"
)

// findReflection returns the reflection point for an image
func findReflection(image []string) (int, bool) {
	walkToEdge := func(lower, upper int) bool {
		for lower >= 0 && upper < len(image) && strings.Compare(image[lower], image[upper]) == 0 {
			lower--
			upper++
		}
		lower++
		return (lower == 0 || upper == len(image))
	}

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

// horizontalReflection returns the reflection point of a horizontal mirror
func horizontalReflection(image img, fn func(image []string) (int, bool)) (int, bool) {
	n, ok := fn(image.raw)
	return n, ok
}

// verticalReflection returns the reflection point of a vertical mirror
func verticalReflection(image img, fn func(image []string) (int, bool)) (int, bool) {
	n, ok := fn(image.transposed())
	return n, ok
}

// one returns a calculation based on reflection points for all images.
func one(lines []string) int {
	parselines(lines)

	sum := 0
	for _, image := range images.img {
		log.Debug("checking for horizontal reflection")
		n, ok := horizontalReflection(image, findReflection)
		if ok {
			sum += 100 * (n + 1)
		}
		log.Debug("checking for vertical reflection")
		n, ok = verticalReflection(image, findReflection)
		if ok {
			sum += (n + 1)
		}
	}

	return sum
}