hdu 3631 多源最短路

这题就是Floyd变形，只要理解了Floyd算法，题目还是不难的。不过我还是WA了一次，原理是在运行Floyd的时候，误加了两个判断，以为当i，j未被标记的时候，i到j的路径不必更新，其实这是错的，去掉以后就过了。

/*
 * hdu3631/win.cpp
 * Created on: 2011-9-6
 * Author    : ben
 */
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;

const int SIZE = 310;
const int MAX = 0x7fffffff;
int map[SIZE][SIZE];
bool marked[SIZE];
int N, M;
void init() {
    int i, j, temp;
    for (i = 0; i < N; i++) {
        for (j = 0; j < N; j++) {
            map[i][j] = MAX;
        }
        map[i][i] = 0;
    }
    for (int k = 0; k < M; k++) {
        scanf("%d%d%d", &i, &j, &temp);
        if (map[i][j] > temp) {
            map[i][j] = temp;
        }
    }
}

void Floyd(int k) {
    int i, j;
    for (i = 0; i < N; i++) {
        for (j = 0; j < N; j++) {
            if (map[i][k] < map[i][j] - map[k][j]) {
                map[i][j] = map[i][k] + map[k][j];
            }
        }
    }
}

void work() {
    int T = 0, op, a, b, Q;
    while (scanf("%d%d%d", &N, &M, &Q) == 3) {
        if (N == 0 && M == 0 && Q == 0) {
            break;
        }
        if (T > 0) {
            putchar('\n');
        }
        printf("Case %d:\n", ++T);
        init();
        memset(marked, false, sizeof(marked));
        for (int i = 0; i < Q; i++) {
            scanf("%d", &op);
            if (op == 0) {
                scanf("%d", &a);
                if (marked[a]) {
                    printf("ERROR! At point %d\n", a);
                } else {
                    marked[a] = true;
                    Floyd(a);
                }
            } else {
                scanf("%d%d", &a, &b);
                if (marked[a] && marked[b]) {
                    if (map[a][b] == 0x7fffffff) {
                        puts("No such path");
                    } else {
                        printf("%d\n", map[a][b]);
                    }
                } else {
                    printf("ERROR! At path %d to %d\n", a, b);
                }
            }
        }
    }
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif
    work();
    return 0;
}