adventofcode/2015/day09/main.go

package main

import (
	"fmt"
	"io"
	"log"
	"os"
	"strconv"
	"strings"
)

var allTowns map[string]roads

type roads map[string]int

func main() {
	allTowns = make(map[string]roads)
	var input []string
	var readInp, bldInput string
	for {
		_, err := fmt.Scan(&readInp)
		if err != nil {
			if err != io.EOF {
				log.Fatal(err)
			}
			break
		}

		if strings.HasSuffix(bldInput, "=") {
			bldInput = bldInput + " " + readInp
			input = append(input, bldInput)
			bldInput = ""
			continue
		}
		if len(bldInput) > 0 {
			bldInput += " "
		}
		bldInput = bldInput + readInp
	}

	for i := range input {
		dirTowns := strings.Split(input[i], " to ")
		secondPart := strings.Split(dirTowns[1], " = ")
		town1 := dirTowns[0]
		town2 := secondPart[0]
		distance := mustAtoi(secondPart[1])
		buildRoute(town1, town2, distance)
	}

	// All routes should be built, find the shortest
	var shortestRoute []string
	shortestDistance := -1
	for i := range allTowns {
		var visited []string
		lastVisit := i
		tripDistance := 0
		for len(visited) < len(allTowns) {
			var dist int
			visited = append(visited, lastVisit)
			lastVisit, dist = findShortest(lastVisit, visited)
			if dist > 0 {
				tripDistance += dist
			}
		}
		if shortestDistance == -1 || tripDistance < shortestDistance {
			shortestDistance = tripDistance
			shortestRoute = visited
		}
	}

	// Now find the longest
	var longestRoute []string
	longestDistance := -1
	for i := range allTowns {
		var visited []string
		lastVisit := i
		tripDistance := 0
		for len(visited) < len(allTowns) {
			var dist int
			visited = append(visited, lastVisit)
			lastVisit, dist = findLongest(lastVisit, visited)
			if dist > 0 {
				tripDistance += dist
			}
		}
		if longestDistance == -1 || tripDistance > longestDistance {
			longestDistance = tripDistance
			longestRoute = visited
		}
	}

	fmt.Println("Shortest Route:" + strconv.Itoa(shortestDistance))
	fmt.Println(strings.Join(shortestRoute, "->"))
	fmt.Println("Longest Route:" + strconv.Itoa(longestDistance))
	fmt.Println(strings.Join(longestRoute, "->"))
}

func findShortest(from string, exclude []string) (string, int) {
	var toTown string
	shortest := -1
	for j := range allTowns[from] {
		var didIt bool
		for ex := range exclude {
			if j == exclude[ex] {
				didIt = true
				break
			}
		}
		if didIt {
			continue
		}
		// Find the quickest trip from here
		if shortest == -1 || allTowns[from][j] < shortest {
			shortest = allTowns[from][j]
			toTown = j
		}
	}
	return toTown, shortest
}

func findLongest(from string, exclude []string) (string, int) {
	var toTown string
	longest := -1
	for j := range allTowns[from] {
		var didIt bool
		for ex := range exclude {
			if j == exclude[ex] {
				didIt = true
				break
			}
		}
		if didIt {
			continue
		}
		// Find the longest trip from here
		if longest == -1 || allTowns[from][j] > longest {
			longest = allTowns[from][j]
			toTown = j
		}
	}
	return toTown, longest
}

func mustAtoi(i string) int {
	var ret int
	var err error
	if ret, err = strconv.Atoi(i); err != nil {
		fmt.Println("Tried to mustAtoi: " + i)
		os.Exit(1)
	}
	return ret
}

func buildRoute(t1, t2 string, dist int) {
	if _, ok := allTowns[t1]; !ok {
		// Add this town
		allTowns[t1] = make(map[string]int)
	}
	allTowns[t1][t2] = dist
	// And the other direction
	if _, ok := allTowns[t2]; !ok {
		// Add this town
		allTowns[t2] = make(map[string]int)
	}
	allTowns[t2][t1] = dist
}