adventofcode/2023/day13/main.go

package main

import (
	"fmt"

	h "git.bullercodeworks.com/brian/adventofcode/helpers"
)

func main() {
	inp := h.StdinToStringSlice()
	part1(inp)
	fmt.Println()
	part2(inp)
}

func part1(input []string) {
	var maps []*h.CoordByteMap
	var wrkInput []string
	bld := func() {
		m := h.StringSliceToCoordByteMap(wrkInput)
		maps = append(maps, &m)
		wrkInput = []string{}
	}
	for i := range input {
		if len(input[i]) == 0 {
			bld()
		} else {
			wrkInput = append(wrkInput, input[i])
		}
	}
	if len(wrkInput) > 0 {
		bld()
	}

	var result int
	for _, m := range maps {
		result += findMirror(m, -1)
	}
	fmt.Println("# Part 1")
	fmt.Println(result)
}

func part2(input []string) {
	var maps []*h.CoordByteMap
	var wrkInput []string
	bld := func() {
		m := h.StringSliceToCoordByteMap(wrkInput)
		maps = append(maps, &m)
		wrkInput = []string{}
	}
	for i := range input {
		if len(input[i]) == 0 {
			bld()
		} else {
			wrkInput = append(wrkInput, input[i])
		}
	}
	if len(wrkInput) > 0 {
		bld()
	}

	var result int
	for _, m := range maps {
		result += checkForSmudge(m)
	}
	fmt.Println("# Part 2")
	fmt.Println(result)
}

func checkForSmudge(m *h.CoordByteMap) int {
	origMirror := findMirror(m, -1)
	for y := m.TLY; y <= m.BRY; y++ {
		for x := m.TLX; x <= m.BRX; x++ {
			orig := m.Get(c(x, y))
			switch orig {
			case '#':
				m.Put(c(x, y), '.')
			case '.':
				m.Put(c(x, y), '#')
			}
			res := findMirror(m, origMirror)
			if res > 0 && res != origMirror {
				return res
			}
			m.Put(c(x, y), orig)
		}
	}
	return 0
}

// findMirror finds a mirror in the map
// returning the value of that mirror (vertical (x+1), horizontal (y+1)* 100)
func findMirror(m *h.CoordByteMap, exclude int) int {
	var found bool
	for x := m.TLX; x <= m.BRX; x++ {
		val := (x + 1)
		if found = checkForVerticalMirror(m, x, x+1); found && val != exclude {
			return x + 1
		}
	}
	for y := m.TLY; y <= m.BRY; y++ {
		val := (y + 1) * 100
		if found = checkForHorizontalMirror(m, y, y+1); found && val != exclude {
			return (y + 1) * 100
		}
	}
	return 0
}

func c(x, y int) h.Coordinate {
	return h.Coordinate{X: x, Y: y}
}

func checkForVerticalMirror(m *h.CoordByteMap, x1, x2 int) bool {
	var wrkX1, wrkX2 int
	for y := m.TLY; y <= m.BRY; y++ {
		wrkX1, wrkX2 = x1, x2
		var match, cont bool
		for wrkX1 >= m.TLX || wrkX2 <= m.BRX {
			if match, cont = hPointsMatch(m, y, wrkX1, wrkX2); match {
				if cont {
					break
				}
				wrkX1--
				wrkX2++
			} else {
				return false
			}
		}
		if cont {
			continue
		}
		if wrkX1 < m.TLX || wrkX2 > m.BRX {
			return false
		}
	}
	// Mirrors _shouldn't_ be at the very edge (or else what are we even doing here)
	if wrkX1 == m.BRX || wrkX2 == m.TLX {
		return false
	}
	return true
}

func hPointsMatch(m *h.CoordByteMap, y, x1, x2 int) (bool, bool) {
	c1, c2 := c(x1, y), c(x2, y)
	// If either is off the map, it could be
	if m.Opt(c1, byte(0)) == 0 || m.Opt(c2, byte(0)) == 0 {
		return true, true
	}
	// Check if (x1, y) == (x2, y)
	v1, v2 := m.Get(c1), m.Get(c2)
	return v1 == v2, false
}

func checkForHorizontalMirror(m *h.CoordByteMap, y1, y2 int) bool {
	var wrkY1, wrkY2 int
	for x := m.TLX; x <= m.BRX; x++ {
		wrkY1, wrkY2 = y1, y2
		var match, cont bool
		for wrkY1 >= m.TLY || wrkY2 <= m.BRY {
			if match, cont = vPointsMatch(m, x, wrkY1, wrkY2); match {
				if cont {
					break
				}
				wrkY1--
				wrkY2++
			} else {
				return false
			}
		}
		if cont {
			continue
		}
		if wrkY1 > m.TLY && wrkY2 < m.BRY {
			return false
		}
	}
	// Mirrors _shouldn't_ be at the very edge (or else what are we even doing here)
	if wrkY1 == m.BRY || wrkY2 == m.TLY {
		return false
	}
	return true
}

func vPointsMatch(m *h.CoordByteMap, x, y1, y2 int) (bool, bool) {
	c1, c2 := c(x, y1), c(x, y2)
	// If either is off the map, it could be
	if m.Opt(c1, byte(0)) == 0 || m.Opt(c2, byte(0)) == 0 {
		return true, true
	}
	// Check if (x, y1) == (x, y2)
	v1, v2 := m.Get(c1), m.Get(c2)
	return v1 == v2, false
}