110 lines
1.7 KiB
Go
110 lines
1.7 KiB
Go
package main
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import (
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"fmt"
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"sort"
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"github.com/jdkaplan/advent-of-code/aoc"
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)
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func main() {
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lines := aoc.Input().ReadLines("day9.txt")
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fmt.Println(part1(lines))
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fmt.Println(part2(lines))
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}
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func part1(lines []string) (risk int) {
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g := NewGrid(lines)
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for r := 0; r < g.Rows; r++ {
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for c := 0; c < g.Cols; c++ {
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risk += g.Risk(r, c)
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}
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}
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return risk
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}
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func part2(lines []string) int {
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g := NewGrid(lines)
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var starts []RC
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for r := 0; r < g.Rows; r++ {
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for c := 0; c < g.Cols; c++ {
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if g.Risk(r, c) != 0 {
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starts = append(starts, RC{r, c})
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}
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}
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}
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var sizes []int
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for _, rc := range starts {
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sizes = append(sizes, g.Flood(rc))
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}
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sort.Sort(sort.Reverse(sort.IntSlice(sizes)))
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return sizes[0] * sizes[1] * sizes[2]
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}
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type RC struct{ r, c int }
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type Grid struct {
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Rows int
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Cols int
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m map[RC]int
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}
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func NewGrid(lines []string) Grid {
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g := Grid{
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m: make(map[RC]int),
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Rows: len(lines),
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Cols: len(lines[0]),
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}
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for r, row := range lines {
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for c, col := range row {
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g.m[RC{r, c}] = int(col - '0')
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}
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}
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return g
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}
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func (g Grid) Risk(r, c int) int {
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rc := RC{r, c}
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v, ok := g.m[rc]
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if !ok {
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return 0
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}
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for _, n := range g.Neighbors(rc) {
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u, ok := g.m[n]
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if ok && u <= v {
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return 0
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}
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}
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return v + 1
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}
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func (g Grid) Neighbors(rc RC) []RC {
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r, c := rc.r, rc.c
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return []RC{
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{r - 1, c},
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{r, c + 1},
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{r + 1, c},
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{r, c - 1},
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}
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}
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func (g Grid) Flood(rc RC) (size int) {
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queue := []RC{rc}
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seen := make(map[RC]bool)
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for len(queue) > 0 {
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rc, queue = queue[0], queue[1:]
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if seen[rc] {
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continue
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}
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for _, n := range g.Neighbors(rc) {
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if v, ok := g.m[n]; ok && v < 9 {
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queue = append(queue, n)
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}
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}
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seen[rc] = true
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size++
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}
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return size
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}
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