/*
 * File: tsp.c
 * Purpose: Tests the naive O(n!) TSP algorithm.
 * Compilation: gcc -o tsp tsp.c
 * Execution: ./tsp
 * Author: San Skulrattanakulchai
 */

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>

#define NUM_CITIES  11
static int dist[][NUM_CITIES] = {
    {0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10},
    {9,  0,  8,  7,  6,  5,  4,  3, 10,  1,  2},
    {8,  7,  0,  6,  5,  4,  3,  2,  9, 10,  1},
    {7,  6,  5,  0,  4,  3,  2,  1,  8,  9, 10},
    {4,  3,  2,  1,  0, 10,  9,  8,  7,  6,  5},
    {10,  9,  8,  7,  6,  0,  5,  4,  3,  2,  1},
    {7,  8,  9, 10,  1,  2,  0,  3,  4,  5,  6},
    {5,  4,  3,  2,  1,  6,  7,  0,  8,  9, 10},
    {10,  9,  8,  7,  6,  5,  4,  3,  0,  2,  1},
    {1,  2,  4,  3,  6,  5,  8,  7, 10,  0,  9},
    {3,  2,  1,  6,  5,  4,  9,  8,  7, 10,  0}
};
static int *pi;
static int minDist;

void swap(int a[], int i, int j) {
    int tmp = a[i];
    a[i] = a[j];
    a[j] = tmp;
}

void perm(int i) {
    int j;
    if (i == NUM_CITIES-1) {
        int d = dist[pi[NUM_CITIES-1]][0];
        for (j = 0; j < NUM_CITIES-1; j++)
            d = d + dist[pi[j]][pi[j+1]];
        if (d < minDist) minDist = d;
    } else for (j = i; j < NUM_CITIES; j++) {
        swap(pi, i, j);
        perm(i+1);
        swap(pi, i, j);
    }
}

void tsp() {
    int i;
    pi = malloc(NUM_CITIES * sizeof(int));
    for (i = 0; i < NUM_CITIES; i++)
        pi[i] = i;
    minDist = INT_MAX;
    perm(1);
    printf("minimum tour length = %d\n", minDist);
}

int main(int argc, char **argv) {
    tsp();
    return 0;
}