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day13.go
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day13.go
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package main
import (
_ "embed"
"fmt"
"github.com/pemoreau/advent-of-code/go/utils/game2d"
"strings"
"time"
)
//go:embed input.txt
var inputDay string
func isVerticalMirror(m game2d.MatrixChar, x int) bool {
diff := min(m.MaxX()-(x+1), x)
for y := 0; y <= m.MaxY(); y++ {
for i := 0; i <= diff; i++ {
if m[y][x+1+i] != m[y][x-i] {
return false
}
}
}
return true
}
func findVerticalMirror(m game2d.MatrixChar, old int) int {
for x := 0; x <= m.MaxX()-1; x++ {
if x+1 != old && isVerticalMirror(m, x) {
return x + 1
}
}
return 0
}
func isHorizontalMirror(m game2d.MatrixChar, y int) bool {
diff := min(m.MaxY()-(y+1), y)
for x := 0; x <= m.MaxX(); x++ {
for i := 0; i <= diff; i++ {
if m[y+1+i][x] != m[y-i][x] {
return false
}
}
}
return true
}
func findHorizontalMirror(m game2d.MatrixChar, old int) int {
for y := 0; y <= m.MaxY()-1; y++ {
if y+1 != old && isHorizontalMirror(m, y) {
return y + 1
}
}
return 0
}
func computeScore(m game2d.MatrixChar) int {
var h = findHorizontalMirror(m, -1)
var v = findVerticalMirror(m, -1)
return v + (h * 100)
}
func trySwap(m game2d.MatrixChar, x, y int, c uint8, h, v int) int {
old := m[y][x]
m[y][x] = c
if nh := findHorizontalMirror(m, h); nh > 0 {
m[y][x] = old
return 100 * nh
} else if nv := findVerticalMirror(m, v); nv > 0 {
m[y][x] = old
return nv
}
m[y][x] = old
return 0
}
func findSmudge(g game2d.MatrixChar) int {
h := findHorizontalMirror(g, -1)
v := findVerticalMirror(g, -1)
for y, l := range g {
for x, c := range l {
switch c {
case '#':
if r := trySwap(g, x, y, '.', h, v); r > 0 {
return r
}
case '.':
if r := trySwap(g, x, y, '#', h, v); r > 0 {
return r
}
default:
panic("invalid char")
}
}
}
panic("no smudge found")
}
func solve(input string, score func(matrix game2d.MatrixChar) int) int {
input = strings.TrimSuffix(input, "\n")
parts := strings.Split(input, "\n\n")
var res int
for _, p := range parts {
m := game2d.BuildMatrixCharFromString(p)
res += score(m)
}
return res
}
func Part1(input string) int {
return solve(input, computeScore)
}
func Part2(input string) int {
return solve(input, findSmudge)
}
func main() {
fmt.Println("--2023 day 13 solution--")
start := time.Now()
fmt.Println("part1: ", Part1(inputDay))
fmt.Println(time.Since(start))
start = time.Now()
fmt.Println("part2: ", Part2(inputDay))
fmt.Println(time.Since(start))
}