hdu 3631 Shortest Path

floyd算法好像很奇妙的样子。可以做到每次加入一个点再以这个点为中间点去更新最短路，效率是n*n。

#include<cstdio>

#include<cstring>

#include<cmath>

#include<vector>

#include<algorithm>

using namespace std;



const int maxn = 305;

const int INF = 0x7FFFFFFF;

int A[maxn][maxn], flag[maxn];

int n, m, q;



void floyd(int x)

{

    int i, j;

    for (i = 0; i < n; i++)

    {

        for (j = 0; j < n; j++)

        {

            if (i == x || j == x) continue;

            if (A[i][x] == INF || A[x][j] == INF) continue;

            if (A[i][x] + A[x][j] < A[i][j]) A[i][j] = A[i][x] + A[x][j];

        }

    }

}



int main()

{

    int i, j, u, v, c, koko = 1;

    while (~scanf("%d%d%d", &n, &m, &q))

    {

        if (n == 0 && m == 0 && q == 0) break;

        memset(flag, 0, sizeof(flag));

        for (i = 0; i <= n; i++)

        {

            for (j = 0; j <= n; j++)

            {

                if (i == j) A[i][j] = 0;

                else A[i][j] = INF;

            }

        }

        for (i = 0; i < m; i++)

        {

            scanf("%d%d%d", &u, &v, &c);

            if (c < A[u][v]) A[u][v] = c;

        }

        int oo, pp, qq;

        if (koko != 1) printf("\n");

        printf("Case %d:\n", koko++);

        for (i = 0; i < q; i++)

        {

            scanf("%d", &oo);

            if (oo == 0)

            {

                scanf("%d", &pp);

                if (flag[pp] == 1) printf("ERROR! At point %d\n", pp);

                else if (flag[pp] == 0){ flag[pp] = 1; floyd(pp); }

            }

            else if (oo == 1)

            {

                scanf("%d%d", &pp, &qq);

                if (flag[pp] == 0 || flag[qq] == 0)printf("ERROR! At path %d to %d\n", pp, qq);

                else

                {

                    if (A[pp][qq] == INF) printf("No such path\n");

                    else printf("%d\n", A[pp][qq]);

                }

            }

        }

    }

    return 0;

}