106 lines
2 KiB
Go
106 lines
2 KiB
Go
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package d9
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import (
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"fmt"
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"sort"
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"strconv"
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"strings"
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)
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func bigger(a byte, b byte) bool {
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aNum, _ := strconv.Atoi(string(a))
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bNum, _ := strconv.Atoi(string(b))
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return aNum > bNum
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}
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func toNum(str byte) int {
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num, _ := strconv.Atoi(string(str))
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return num
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}
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func addWalls(lines []string) []string {
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for i, line := range lines {
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lines[i] = fmt.Sprintf("9%v9", line)
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}
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nines := strings.Repeat("9", len(lines[0]))
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return append([]string{nines}, append(lines, nines)...)
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}
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func D9(in string) int {
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lines := addWalls(strings.Split(strings.TrimSpace(in), "\n"))
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risk := 0
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for i := 1; i < len(lines)-1; i++ {
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for j := 1; j < len(lines[0])-1; j++ {
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current := lines[i][j]
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top := bigger(lines[i-1][j], current)
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right := bigger(lines[i][j+1], current)
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bottom := bigger(lines[i+1][j], current)
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left := bigger(lines[i][j-1], current)
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if top && right && bottom && left {
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risk += toNum(current) + 1
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}
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}
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}
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return risk
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}
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type exists struct{}
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type pos struct {
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x int
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y int
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}
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type basin map[pos]exists
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const wall = '9'
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func flooded(x, y int, basins []basin) bool {
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for _, basin := range basins {
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if _, ok := basin[pos{x, y}]; ok {
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return true
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}
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}
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return false
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}
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func flood(x, y int, heights []string, basin basin) basin {
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if heights[y][x] == wall {
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return basin
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}
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if _, ok := basin[pos{x, y}]; ok {
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return basin
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}
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basin[pos{x, y}] = exists{}
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flood(x, y-1, heights, basin)
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flood(x+1, y, heights, basin)
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flood(x, y+1, heights, basin)
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flood(x-1, y, heights, basin)
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return basin
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}
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func D9P2(in string) int {
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heights := addWalls(strings.Split(strings.TrimSpace(in), "\n"))
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basins := []basin{}
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for y := 1; y < len(heights)-1; y++ {
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for x := 1; x < len(heights[0])-1; x++ {
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if !flooded(x, y, basins) && heights[y][x] != wall {
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basins = append(basins, flood(x, y, heights, basin{}))
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}
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}
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}
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sort.Slice(basins, func(i, j int) bool { return len(basins[i]) > len(basins[j]) })
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return len(basins[0]) * len(basins[1]) * len(basins[2])
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}
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