Programming

#include <stdio.h>

#define GRAPHSIZE 2048
#define INFINITY GRAPHSIZE*GRAPHSIZE
#define MAX(a, b) ((a > b) ? (a) : (b))

int e; /* The number of nonzero edges in the graph */
int n; /* The number of nodes in the graph */
long dist[GRAPHSIZE][GRAPHSIZE]; /* dist[i][j] is the distance between node i and j; or 0 if there is no direct connection */
long d[GRAPHSIZE]; /* d[i] is the length of the shortest path between the source (s) and node i */
int prev[GRAPHSIZE][GRAPHSIZE + 1]; /* prev[i] holds the nodes that could comes right before i in the shortest path from the source to i;
                                        prev[i][0] is the number of nodes and prev[i][1..] are the nodes */

void printD() {
    int i;

    printf("Distances:\n");
    for (i = 1; i <= n; ++i)
        printf("%10d", i);
    printf("\n");
    for (i = 1; i <= n; ++i) {
        printf("%10ld", d[i]);
    }
    printf("\n");
}

/*
 * Prints the shortest path from the source to dest.
 *
 * dijkstra(int) MUST be run at least once BEFORE
 * this is called
 */
void printPath(int dest, int depth) {
    int i, j;

    printf("-%d\n", dest);
    for (i = 1; i <= prev[dest][0]; ++i) {
        for (j = 0; j <= depth; ++j)
            printf(" |");
        printPath(prev[dest][i], depth + 1);
    }
}

void dijkstra(int s) {
    int i, k, mini;
    int visited[GRAPHSIZE];

    for (i = 1; i <= n; ++i) {
        d[i] = INFINITY;
        prev[i][0] = 0; /* no path has yet been found to i */
        visited[i] = 0; /* the i-th element has not yet been visited */
    }

    d[s] = 0;

    for (k = 1; k <= n; ++k) {
        mini = -1;
        for (i = 1; i <= n; ++i)
            if (!visited[i] && ((mini == -1) || (d[i] < d[mini])))
                mini = i;

        visited[mini] = 1;

        for (i = 1; i <= n; ++i)
            if (dist[mini][i]) {
                if (d[mini] + dist[mini][i] < d[i]) { /* a shorter path has been found */
                    d[i] = d[mini] + dist[mini][i];
                    prev[i][0] = 1;
                    prev[i][1] = mini;
                } else if (d[mini] + dist[mini][i] == d[i]) { /* a path of the same length has been found */
                    ++prev[i][0];
                    prev[i][prev[i][0]] = mini;
                }
            }
    }
}

int main(int argc, char *argv[]) {
    int i, j;
    int u, v, w;

    FILE *fin = fopen("dist.txt", "r");
    fscanf(fin, "%d", &e);
    for (i = 0; i < e; ++i)
        for (j = 0; j < e; ++j)
            dist[i][j] = 0;
    n = -1;
    for (i = 0; i < e; ++i) {
        fscanf(fin, "%d%d%d", &u, &v, &w);
        dist[u][v] = w;
        n = MAX(u, MAX(v, n));
    }
    fclose(fin);

    dijkstra(1);

    printD();

    printf("\n");
    for (i = 1; i <= n; ++i) {
        printf("Path to %d:\n", i);
        printPath(i, 0);
        printf("\n");
    }

    return 0;
}