103 lines
2.1 KiB
Go
103 lines
2.1 KiB
Go
package main
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import (
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"bufio"
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"fmt"
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"os"
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"strings"
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)
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func main() {
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fmt.Println(find(readData("example.txt")))
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fmt.Println(36, 81)
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fmt.Println(find(readData("data.txt")))
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}
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type Candidate struct {
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X, Y int
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Alt byte
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Head *TrailHead
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}
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func (c Candidate) Identity() int {
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return (c.X << 16) | c.Y
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}
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type TrailHead struct {
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Reaches map[int]bool
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}
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func findNextCandidates(x, y int, targetAlt byte, head *TrailHead, topo [][]byte) (result []Candidate) {
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if x > 0 && topo[y][x-1] == targetAlt {
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result = append(result, Candidate{x - 1, y, targetAlt, head})
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}
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if x < len(topo[y])-1 && topo[y][x+1] == targetAlt {
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result = append(result, Candidate{x + 1, y, targetAlt, head})
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}
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if y > 0 && topo[y-1][x] == targetAlt {
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result = append(result, Candidate{x, y - 1, targetAlt, head})
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}
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if y < len(topo)-1 && topo[y+1][x] == targetAlt {
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result = append(result, Candidate{x, y + 1, targetAlt, head})
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}
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return
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}
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func find(topo [][]byte) (resultPart1, resultPart2 int) {
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candidates := make([]Candidate, 0)
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for y, line := range topo {
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for x, alt := range line {
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if alt == 0 {
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trailhead := &TrailHead{make(map[int]bool)}
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candidate := Candidate{x, y, alt, trailhead}
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candidates = append(candidates, candidate)
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}
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}
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}
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for len(candidates) > 0 {
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current := candidates[len(candidates)-1]
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candidates = candidates[:len(candidates)-1]
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nextCandidates := findNextCandidates(current.X, current.Y, current.Alt+1, current.Head, topo)
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if current.Alt == 8 {
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for _, summit := range nextCandidates {
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id := summit.Identity()
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_, alreadyIn := summit.Head.Reaches[id]
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if !alreadyIn {
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summit.Head.Reaches[id] = true
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resultPart1++
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}
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}
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resultPart2 += len(nextCandidates)
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} else {
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candidates = append(candidates, nextCandidates...)
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}
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}
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return
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}
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func readData(fileName string) (topo [][]byte) {
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fp, err := os.Open(fileName)
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if err != nil {
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panic(err)
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}
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scanner := bufio.NewScanner(fp)
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for scanner.Scan() {
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line := []byte(strings.TrimSpace(scanner.Text()))
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if len(line) == 0 {
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continue
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}
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for i := range line {
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line[i] = line[i] - '0'
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}
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topo = append(topo, line)
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}
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return
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}
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