Advent-of-Code-2023/day25/graph.go

package day25

import (
	"fmt"
	"log"
	"os"
	"strings"

	mapset "github.com/deckarep/golang-set/v2"
)

type Graph struct {
	Nodes map[string]*Node
}

type Node struct {
	Name      string
	Neighbors mapset.Set[string]
}

func (n Node) String() string {
	return fmt.Sprintf("[%s : %+v]", n.Name, n.Neighbors)
}

func ReadGraphFile(filename string) (g Graph) {
	g.Nodes = map[string]*Node{}

	bytes, err := os.ReadFile(filename)
	if err != nil {
		panic(err)
	}
	text := strings.TrimSpace(string(bytes))
	for _, line := range strings.Split(text, "\n") {
		g.readGraphLine(line)
	}

	return
}

func (g *Graph) readGraphLine(l string) (n Node) {
	firstSplit := strings.Split(l, ":")
	n.Name = firstSplit[0]
	n.Neighbors = mapset.NewSet[string]()

	secondSplit := strings.Fields(firstSplit[1])

	for _, neighborName := range secondSplit {
		neighbor, exists := g.Nodes[neighborName]
		if !exists {
			neighbor = &Node{
				Name:      neighborName,
				Neighbors: mapset.NewSet[string](),
			}
			g.Nodes[neighborName] = neighbor
		}
		neighbor.Neighbors.Add(n.Name)
		n.Neighbors.Add(neighbor.Name)
	}

	g.Nodes[n.Name] = &n

	return
}

func (g *Graph) RemoveEdge(a, b string) {
	// log.Printf("entering remove edge for %s and %s", a, b)
	nodeA, existsA := g.Nodes[a]
	// log.Println("got first node", nodeA, existsA)
	nodeB, existsB := g.Nodes[b]
	// log.Println("got second node", nodeB, existsB)
	if !existsA || !existsB {
		panic("requesting not found node")
	}

	// log.Println("before removals")
	newANeighbors := mapset.NewSet[string]()
	for oldNeighbor := range nodeA.Neighbors.Iter() {
		if oldNeighbor != nodeB.Name {
			newANeighbors.Add(oldNeighbor)
		}
	}
	nodeA.Neighbors = newANeighbors
	// 	nodeA.Neighbors.Remove(nodeB.Name)

	// log.Println("removed first", nodeA)
	newBNeighbors := mapset.NewSet[string]()
	for oldNeighbor := range nodeB.Neighbors.Iter() {
		if oldNeighbor != nodeB.Name {
			newBNeighbors.Add(oldNeighbor)
		}
	}
	nodeB.Neighbors = newBNeighbors
	// nodeB.Neighbors.Remove(nodeA.Name)
	// log.Println("removed second", nodeB)
}

func (g *Graph) findCycle() (from, to string, exists bool) {
	log.Printf(">>>> starting new find cycle")
	var firstNode *Node
	for _, n := range g.Nodes {
		firstNode = n
		break
	}
	initialVisited := mapset.NewSet[string](firstNode.Name)
	for neighborName := range firstNode.Neighbors.Iter() {
		from, to, exists = g.dfcCycle(firstNode.Name, neighborName, initialVisited)
		if exists {
			break
		}
	}

	log.Printf("<<<< cycle %t, from %s to %s", exists, from, to)
	return
}

func (g *Graph) dfcCycle(fromName, atName string, visited mapset.Set[string]) (cycleFrom, cycleTo string, cycleExists bool) {
	// log.Printf("> step from %+v to %+v. visited : %+v", fromName, atName, visited)
	if visited.Cardinality() == len(g.Nodes) {
		return
	}

	atNode := g.Nodes[atName]

	if visited.Contains(atName) {
		return fromName, atName, true
	}

	newVisited := visited.Clone()
	newVisited.Add(atName)
	for neighborName := range atNode.Neighbors.Iter() {
		cycleFrom, cycleTo, cycleExists = g.dfcCycle(atName, neighborName, newVisited)
		if cycleExists {
			break
		}
	}

	return
}

func (g *Graph) DoThreeRemovals() {
	from, to, found := g.findCycle()
	log.Printf("first result %s, %s, %t", from, to, found)
	//     graph_test.go:26: first result xhk, rhn, true
	g.RemoveEdge("xhk", "rhn")

	from, to, found = g.findCycle()
	log.Printf("second result %s, %s, %t", from, to, found)
	//     graph_test.go:32: second result qnr, nvd, true
	g.RemoveEdge("qnr", "nvd")

	from, to, found = g.findCycle()
	log.Printf("third result %s, %s, %t", from, to, found)
	//     graph_test.go:36: third result lhk, cmg, true

	g.RemoveEdge("lhk", "cmg")
	from, to, found = g.findCycle()
	log.Printf("fourth result %s, %s, %t", from, to, found)

	// OK, so there could be more than 3 cycles.
	// but if i want to break things into 2 components, i need to do more investigating
	return
}

func (g *Graph) ComponentFrom(fromName string) (component mapset.Set[string]) {
	startNode := g.Nodes[fromName]
	component = mapset.NewSet[string](startNode.Name)
	toVisit := startNode.Neighbors.Clone()

	for toVisit.Cardinality() > 0 {
		runnerNodeName, _ := toVisit.Pop()
		if component.Contains(runnerNodeName) {
			continue
		}
		component.Add(runnerNodeName)
		runnerNode := g.Nodes[runnerNodeName]
		unvisitedNeighbors := runnerNode.Neighbors.Difference(component)
		// log.Printf("adding %s to component. neighbors %+v, adding %+v to visit",
		// 	runnerNodeName, runnerNode.Neighbors, unvisitedNeighbors)
		toVisit = toVisit.Union(unvisitedNeighbors)
	}

	return
}

func (g *Graph) ToMermaid() (result string) {
	result += "flowchart TD\n"
	edges := mapset.NewSet[string]()

	for _, node := range g.Nodes {
		for neighborName := range node.Neighbors.Iter() {
			var first, second string
			if node.Name < neighborName {
				first = node.Name
				second = neighborName
			} else {
				first = neighborName
				second = node.Name
			}
			edges.Add(fmt.Sprintf("\t%s --- %s\n", first, second))
		}
	}

	for line := range edges.Iter() {
		result += line
	}
	return
}

func (g *Graph)SaveAsMermaid(filename string) {
	mmd := g.ToMermaid()

	file, err := os.Create(filename)
	if err != nil {
		panic(err)
	}
	defer func() {
		if err := file.Close(); err != nil {
			panic(err)
		}
	}()

	file.WriteString(mmd)
}

type Edge struct {
	smaller, bigger string
}

func CreateEdge(a, b string) Edge {
	var smaller, bigger string
	if a < b {
		smaller = a
		bigger = b
	} else {
		smaller = b
		bigger = a
	}
	return Edge{smaller, bigger}
}

func (g *Graph) RemoveAllCycles() (removedEdges mapset.Set[Edge]) {
	removedEdges = mapset.NewSet[Edge]()
	hasCycle := true
	var from, to string
	for hasCycle {
		from, to, hasCycle = g.findCycle()
		if hasCycle {
			edgeToRemove := CreateEdge(from, to)
			removedEdges.Add(edgeToRemove)
			g.RemoveEdge(from, to)
		}
	}
	return
}