aoc2023/day25/day25.go

package day25

import (
	"fmt"
	"strings"

	"gitea.paas.celticinfo.fr/oabrivard/aoc2023/utils"
)

type Graph map[string]map[string]bool
type Edge struct {
	left  string
	right string
}

func buildGraph(lines []string) Graph {
	graph := map[string]map[string]bool{}

	for _, line := range lines {
		parts := strings.Split(line, ":")

		src := parts[0]
		if _, found := graph[src]; !found {
			graph[src] = map[string]bool{}
		}
		links := graph[src]

		dests := strings.Fields(strings.TrimSpace(parts[1]))
		for _, dst := range dests {
			links[dst] = true

			if _, found := graph[dst]; !found {
				graph[dst] = map[string]bool{}
			}
			reverseLink := graph[dst]
			reverseLink[src] = true
		}
	}

	return graph
}

func printGraph(graph Graph) {
	for k1, v1 := range graph {
		fmt.Print(k1, ": ")
		for k2 := range v1 {
			fmt.Print(k2, " ")
		}
		fmt.Println("")
	}
}

func countComponents(graph Graph) int {
	visited := map[string]bool{}
	count := 0

	for node := range graph {
		if !visited[node] {
			count++
			queue := utils.NewQueue[string]()
			queue.Enqueue(node)

			for queue.HasElement() {
				curNode := queue.Dequeue()
				visited[curNode] = true

				for linkedNode := range graph[curNode] {
					if !visited[linkedNode] {
						queue.Enqueue(linkedNode)
					}
				}
			}
		}
	}
	return count
}

func buildVerticesLists(graph Graph) []map[string]bool {
	visited := map[string]bool{}
	result := []map[string]bool{}
	currSubgraph := 0

	for node := range graph {
		if !visited[node] {
			result = append(result, map[string]bool{})
			result[currSubgraph][node] = true

			queue := utils.NewQueue[string]()
			queue.Enqueue(node)

			for queue.HasElement() {
				curNode := queue.Dequeue()
				visited[curNode] = true
				result[currSubgraph][curNode] = true

				for linkedNode := range graph[curNode] {
					if !visited[linkedNode] {
						queue.Enqueue(linkedNode)
					}
				}
			}
			currSubgraph++
		}
	}
	return result
}

func buildEdgeList(graph Graph) []Edge {
	edges := map[Edge]bool{}

	for node, connectedNodes := range graph {
		for connectedNode := range connectedNodes {
			_, found1 := edges[Edge{node, connectedNode}]
			_, found2 := edges[Edge{connectedNode, node}]

			if !found1 && !found2 {
				edges[Edge{node, connectedNode}] = true
			}
		}
	}

	result := []Edge{}
	for e := range edges {
		result = append(result, e)
	}
	return result
}

func findEdgesToDelete(graph Graph, edges []Edge) (bool, *Edge, *Edge, *Edge) {
	for i := 0; i < len(edges); i++ {
		for j := i + 1; j < len(edges); j++ {
			for k := j + 1; k < len(edges); k++ {
				// Delete edges i, j and k from graph
				delete(graph[edges[i].left], edges[i].right)
				delete(graph[edges[i].right], edges[i].left)
				delete(graph[edges[j].left], edges[j].right)
				delete(graph[edges[j].right], edges[j].left)
				delete(graph[edges[k].left], edges[k].right)
				delete(graph[edges[k].right], edges[k].left)

				// count components
				count := countComponents(graph)

				// restore Graph
				graph[edges[i].left][edges[i].right] = true
				graph[edges[i].right][edges[i].left] = true
				graph[edges[j].left][edges[j].right] = true
				graph[edges[j].right][edges[j].left] = true
				graph[edges[k].left][edges[k].right] = true
				graph[edges[k].right][edges[k].left] = true

				if count == 2 {
					return true, &edges[i], &edges[j], &edges[k]
				}
			}
		}
	}

	return false, nil, nil, nil
}

func Part1(lines []string) int {
	graph := buildGraph(lines)
	printGraph(graph)
	edges := buildEdgeList(graph)
	fmt.Println(edges)
	success, edge1, edge2, edge3 := findEdgesToDelete(graph, edges)

	if !success {
		return 0
	}

	fmt.Println(*edge1)
	fmt.Println(*edge2)
	fmt.Println(*edge3)

	delete(graph[edge1.left], edge1.right)
	delete(graph[edge1.right], edge1.left)
	delete(graph[edge2.left], edge2.right)
	delete(graph[edge2.right], edge2.left)
	delete(graph[edge3.left], edge3.right)
	delete(graph[edge3.right], edge3.left)

	result := buildVerticesLists(graph)

	fmt.Println(result[0])
	fmt.Println(result[1])

	return len(result[0]) * len(result[1])
}