adventofcode/2023/day25/main.go

package main

import (
	"fmt"
	"math/rand"
	"strings"

	h "git.bullercodeworks.com/brian/adventofcode/helpers"
)

type component struct {
	id          string
	connections map[string]component
	conns       map[string]bool
}

type components struct {
	all   map[string]component
	edges []connections
}

type connections struct {
	from, to string
	track    []string
}

func main() {
	lines := h.StdinToStringSlice()

	var comps components
	var edges []connections
	var counter int
	var tries int
	for tries < 100 {
		counter = 0
		for {
			counter++
			compsS := components{all: make(map[string]component)}
			for _, line := range lines {
				connect(&compsS, line)
			}
			cc := minCut(compsS)
			cuts := len(cc.edges)
			edges = cc.edges
			comps = compsS
			if cuts == 3 {
				break
			}
			if counter >= 100 {
				break
			}
		}
		tries++
		if counter < 100 {
			break
		}
	}

	total := cutInGroups(&comps, edges)
	fmt.Println(total)
}

func connect(comps *components, line string) {
	split := strings.Split(line, ": ")
	nodeName := split[0]
	connectionsNames := strings.Split(split[1], " ")

	node := component{id: nodeName, connections: make(map[string]component), conns: make(map[string]bool)}
	if _, ok := comps.all[nodeName]; !ok {
		comps.all[nodeName] = node
	}
	for _, neighborName := range connectionsNames {
		neighbor := component{id: neighborName, connections: make(map[string]component), conns: make(map[string]bool)}
		if _, ok := comps.all[neighborName]; !ok {
			comps.all[neighborName] = neighbor
		}
		comps.all[nodeName].connections[neighborName] = neighbor
		comps.all[nodeName].conns[neighborName] = true
		comps.all[neighborName].connections[nodeName] = node
		comps.all[neighborName].conns[nodeName] = true
		comps.edges = append(comps.edges, connections{
			from:  nodeName,
			to:    neighborName,
			track: []string{nodeName, neighborName},
		})
	}
}

func minCut(comps components) components {
	cc := components{
		all:   make(map[string]component),
		edges: comps.edges,
	}
	for key, val := range comps.all {
		cc.all[key] = val
	}

	for len(cc.all) > 2 {
		u, v := randomComps(&cc)
		contract(&cc, u, v)
	}

	return cc
}

func randomComps(comps *components) (component, component) {
	randomN := rand.Intn(len(comps.edges))
	edge := comps.edges[randomN]
	comps.edges = append(comps.edges[:randomN], comps.edges[randomN+1:]...)
	randCorn := rand.Intn(2)
	var nameU, nameV string
	if randCorn == 0 {
		nameU = edge.from
		nameV = edge.to
	} else {
		nameU = edge.to
		nameV = edge.from
	}
	u, v := comps.all[nameU], comps.all[nameV]
	return u, v
}

func contract(comps *components, u component, v component) {
	delete(comps.all, v.id)
	delete(comps.all[u.id].connections, v.id)
	for _, node := range comps.all {
		if _, ok := node.connections[v.id]; ok {
			delete(node.connections, v.id)
			node.connections[u.id] = u
			comps.all[u.id].connections[node.id] = node
		}
	}
	for i := 0; i < len(comps.edges); {
		if comps.edges[i].from == v.id {
			comps.edges[i].from = u.id
		}
		if comps.edges[i].to == v.id {
			comps.edges[i].to = u.id
		}
		if comps.edges[i].from == comps.edges[i].to {
			comps.edges = append(comps.edges[:i], comps.edges[i+1:]...)
			continue
		}
		i++
	}
}

func cutInGroups(comps *components, edges []connections) int {
	var final1, final2 string
	for i, edge := range edges {
		cut1 := edge.track[0]
		cut2 := edge.track[1]
		delete(comps.all[cut1].conns, cut2)
		delete(comps.all[cut2].conns, cut1)
		if i == len(edges)-1 {
			final1 = cut1
			final2 = cut2
		}
	}
	group1 := countN(comps, final1)
	group2 := countN(comps, final2)
	return group1 * group2
}

func countN(comps *components, start string) int {
	visited := make(map[string]bool)
	counter := 0
	entry := start
	path := []string{entry}
	for len(path) > 0 {
		currentPath := path[0]
		path = path[1:]
		if _, ok := visited[currentPath]; ok {
			continue
		}
		counter++
		currentcomponent := comps.all[currentPath]
		visited[currentPath] = true
		for key := range currentcomponent.conns {
			if _, ok := visited[key]; ok {
				continue
			}
			path = append(path, key)
		}
	}
	return counter
}