/
tsp.go
310 lines (276 loc) · 7.51 KB
/
tsp.go
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/* vim: set filetype=go : */
package main
import (
"fmt"
"io/ioutil"
"os"
"rand"
"sort"
"strconv"
"strings"
"time"
)
func loadInstance(path string) (matrix [][]int) {
b, err := ioutil.ReadFile(path)
if err != nil {
fmt.Println(err)
return
}
var (
started bool
row, column int
)
for _, line := range strings.Split(string(b), "\n", -1) {
fields := strings.Fields(line)
if len(fields) > 0 {
if !started {
if fields[0] == "DIMENSION:" {
n, err := strconv.Atoi(fields[1])
if err != nil {
fmt.Println(err)
}
matrix = make([][]int, n)
for i := 0; i < n; i++ {
matrix[i] = make([]int, n)
}
}
if fields[0] == "EDGE_WEIGHT_SECTION" {
started = true
}
} else {
if fields[0] == "EOF" {
break
}
for _, v := range fields {
matrix[column][row], err = strconv.Atoi(v)
if err != nil {
fmt.Println(err)
return
}
row++
if row == len(matrix) {
row = 0
column++
}
}
}
}
}
return
}
func random(matrix [][]int) (tour []int, best int) {
const maxIters = 1e6
best = 1e6
for i := 0; i < maxIters; i++ {
perm := rand.Perm(len(matrix))
length := matrix[perm[len(matrix)-1]][perm[0]]
for j := 1; j < len(matrix); j++ {
length += matrix[perm[j-1]][perm[j]]
}
if length < best {
tour, best = perm, length
}
}
return
}
func heuristic(matrix [][]int) (tour []int, best int) {
best = 1e6
free := make(map[int]bool)
for i := 0; i < len(matrix); i++ {
for j := 0; j < len(matrix); j++ {
free[j] = j != i
}
curr := make([]int, len(matrix))
curr[0] = i
index := 0
total := 0
for index + 1 < len(matrix) {
var min int = 1e6
var argmin int
for j := 0; j < len(matrix); j++ {
if free[j] {
dist := matrix[curr[index]][j]
if dist < min {
min = dist
argmin = j
}
}
}
index++
curr[index] = argmin
free[argmin] = false
total += min
}
total += matrix[curr[len(matrix)-1]][curr[0]]
if total < best {
tour, best = curr, total
}
}
return
}
type arc struct {
u, v int
}
type neigh struct {
i, j, delta int
}
type neighbourhood []neigh
func (n neighbourhood) Len() int {
return len(n)
}
func (n neighbourhood) Less(i, j int) bool {
return n[i].delta < n[j].delta
}
func (n neighbourhood) Swap(i, j int) {
n[i], n[j] = n[j], n[i]
}
func n2opt(matrix [][]int, arcs []arc, greedy bool) (neighs neighbourhood) {
n := len(matrix)
neighs = make(neighbourhood, 0)
for i := 0; i < n; i++ {
for j := 0; j < n; j++ {
if i == j {
continue
}
delta := 0
delta -= matrix[arcs[i].u][arcs[i].v]
delta -= matrix[arcs[j].u][arcs[j].v]
delta += matrix[arcs[i].u][arcs[j].u]
delta += matrix[arcs[i].v][arcs[j].v]
for k := (i+1)%n; k != j; k = (k+1)%n {
delta -= matrix[arcs[k].u][arcs[k].v]
delta += matrix[arcs[k].v][arcs[k].u]
}
if greedy && delta < 0 {
neighs = []neigh{neigh{i, j, delta}}
return
}
neighs = append(neighs, neigh{i, j, delta})
}
}
sort.Sort(neighs)
return
}
func path2arcs(path []int) (arcs []arc) {
n := len(path)
arcs = make([]arc, n)
for i := 0; i < n; i++ {
arcs[i] = arc{path[i], path[(i+1)%n]}
}
return
}
func applyMove(in []arc, move neigh) (out []arc) {
out = make([]arc, len(in))
i, j, k, n := move.i, move.j, 0, len(in)
out[k] = arc{in[i].u, in[j].u}
k++
for l := (j-1+n)%n; l != i; l = (l-1+n)%n {
out[k] = arc{in[l].v, in[l].u}
k++
}
out[k] = arc{in[i].v, in[j].v}
k++
for l := (j+1)%n; l != i; l = (l+1)%n {
out[k] = in[l]
k++
}
return
}
func arcs2path(arcs []arc) (path []int) {
path = make([]int, len(arcs))
for i, arc := range arcs {
path[i] = arc.u
}
return
}
func localSearch(matrix [][]int, greedy bool) (path []int, best int) {
path, best = heuristic(matrix[:])
arcs := path2arcs(path[:])
for {
n := n2opt(matrix[:], arcs[:], greedy)
if n[0].delta >= 0 {
break
}
arcs = applyMove(arcs[:], n[0])
best += n[0].delta
}
path = arcs2path(arcs[:])
return
}
func steepest(matrix [][]int) (path []int, best int) {
return localSearch(matrix[:], false)
}
func greedy(matrix [][]int) (path []int, best int) {
return localSearch(matrix[:], true)
}
var maxIters int
var tabuLength int
var tabuList []int
func isTabu(arcs []arc, move neigh, iter int) (result bool) {
result = iter - tabuList[arcs[move.i].u] < tabuLength
result = result || iter - tabuList[arcs[move.i].v] < tabuLength
result = result || iter - tabuList[arcs[move.j].u] < tabuLength
result = result || iter - tabuList[arcs[move.j].v] < tabuLength
return
}
func makeTabu(arcs []arc, move neigh, iter int) {
tabuList[arcs[move.i].u] = iter
tabuList[arcs[move.i].v] = iter
tabuList[arcs[move.j].u] = iter
tabuList[arcs[move.j].v] = iter
}
func tabuSearch(matrix [][]int) (path []int, best int) {
path = make([]int, len(matrix))
best = 0
for i := 0; i < len(matrix); i++ {
path[i] = i
best += matrix[i][(i+1)%len(matrix)]
}
path, best = heuristic(matrix[:])
arcs := path2arcs(path[:])
maxIters = 1 << 8
tabuList = make([]int, len(matrix))
tabuLength = len(matrix)
iter := 0
curr := best
for i := 0; i < maxIters; i++ {
n := n2opt(matrix[:], arcs[:], false)
for _, v := range n {
if !isTabu(arcs[:], v, iter) || curr + v.delta < best {
makeTabu(arcs[:], v, iter)
arcs = applyMove(arcs[:], v)
curr += v.delta
if v.delta < 0 {
if curr < best {
best = curr
path = arcs2path(arcs[:])
}
// i = 0
}
break
}
}
iter++
}
return
}
func main() {
if len(os.Args) != 3 {
fmt.Println("Usage: ./tsp <INSTANCE> <ALGORITHM>")
return
}
algs := make(map[string] func([][]int) ([]int, int))
algs["RANDOM"] = random
algs["HEURISTIC"] = heuristic
algs["STEEPEST"] = steepest
algs["GREEDY"] = greedy
algs["TABU"] = tabuSearch
if _, ok := algs[os.Args[2]]; !ok {
fmt.Println("Unknown algorithm:", os.Args[2])
return
}
rand.Seed(time.Seconds())
matrix := loadInstance(os.Args[1])
tour, best := algs[os.Args[2]](matrix[:])
fmt.Println(best, tour)
}