aoc21/15/main.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"strconv"
)

type Graph struct {
	nodes      map[Node]int
	neighbours map[Node]map[Node]bool
}

type Node struct {
	x, y int
}

const expansions = 1

func main() {
	file, err := os.Open("input.txt")
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)
	scanner.Split(bufio.ScanLines)

	var grid [][]int
	graph := Graph{make(map[Node]int), make(map[Node]map[Node]bool)}

	var y int
	for scanner.Scan() {
		line := scanner.Text()
		if y == 0 {
			grid = make([][]int, len(line)*expansions)
			for i := range grid {
				grid[i] = make([]int, len(line)*expansions)
			}
		}
		for x, char := range line {
			num, _ := strconv.Atoi(string(char))

			for expandY := 0; expandY < expansions; expandY++ {
				for expandX := 0; expandX < expansions; expandX++ {
					expandNum := num + expandX + expandY
					if expandNum >= 10 {
						expandNum = (expandNum % 10) + 1
					}
					yPoint, xPoint := y+len(line)*expandY, x+len(line)*expandX
					grid[yPoint][xPoint] = expandNum
					node := Node{xPoint, yPoint}
					graph.nodes[node] = grid[yPoint][xPoint]
				}
			}
		}
		y++
	}

	for y := 0; y < len(grid); y++ {
		for x := 0; x < len(grid[0]); x++ {
			node := Node{x, y}
			if graph.neighbours[node] == nil {
				graph.neighbours[node] = make(map[Node]bool)
			}

			if x+1 < len(grid[0]) {
				nextXNode := Node{x + 1, y}
				if graph.neighbours[nextXNode] == nil {
					graph.neighbours[nextXNode] = make(map[Node]bool)
				}
				graph.neighbours[node][nextXNode] = true
				graph.neighbours[nextXNode][node] = true
			}

			if y+1 < len(grid) {
				nextYNode := Node{x, y + 1}
				if graph.neighbours[nextYNode] == nil {
					graph.neighbours[nextYNode] = make(map[Node]bool)
				}
				graph.neighbours[node][nextYNode] = true
				graph.neighbours[nextYNode][node] = true
			}
		}
	}

	target := Node{len(grid) - 1, len(grid) - 1}
	dist := dijkstra(graph, Node{0, 0}, target)

	fmt.Println(dist[target])
}

func dijkstra(g Graph, source Node, target Node) (dist map[Node]int) {
	Q := make(map[Node]bool)
	dist = make(map[Node]int)
	prev := make(map[Node]Node)

	for v := range g.nodes {
		dist[v] = 0x7fffffffffffffff
		Q[v] = true
	}
	dist[source] = 0

	for len(Q) > 0 {

		minInQ := 0x7fffffffffffffff
		var v Node
		for node := range Q {
			if dist[node] < minInQ {
				v = node
				minInQ = dist[node]
			}
		}
		delete(Q, v)

		if v == target {
			S := make([]Node, 0)
			u := target

			if _, ok := prev[u]; ok || u == source {
				for u != (Node{}) {
					S = append([]Node{u}, S...)
					u = prev[u]
				}
				fmt.Println()
			}
		}

		for u := range g.neighbours[v] {
			if _, ok := Q[u]; !ok {
				continue
			}
			alt := dist[v] + g.nodes[u]
			if alt < dist[u] {
				dist[u] = alt
				prev[v] = u
			}
		}
	}
	return
}