（最小生成树）Constructing Roads -- poj -- 2421

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

const int N = 110;
const int INF = 0xfffffff;

int n, J[N][N], dist[N], vis[N];

int Prim()
{
    int i, j, ans=0;
    dist[1]=0;
    memset(vis, 0, sizeof(vis));
    vis[1]=1;

    for(i=1; i<=n; i++)
        dist[i]=J[1][i];

    for(i=1; i<n; i++)
    {
        int index=1, MIN=INF;
        for(j=1; j<=n; j++)
        {
            if(!vis[j] && dist[j]<MIN)
            {
                index=j; MIN=dist[j];
            }
        }
        vis[index]=1;
        ans += MIN;
        for(j=1; j<=n; j++)
        {
            if(!vis[j] && dist[j]>J[index][j])
                dist[j]=J[index][j];
        }
    }
    return ans;
}

int main ()
{
    while(scanf("%d", &n)!=EOF)
    {
        int i, j;

        memset(J, 0, sizeof(J));

        for(i=1; i<=n; i++)
        for(j=1; j<=n; j++)
        scanf("%d", &J[i][j]);

        int m, a, b;
        scanf("%d", &m);
        for(i=1; i<=m; i++)
        {
            scanf("%d%d", &a, &b);
            J[a][b]=J[b][a]=0;
        }

        int ans=Prim();

        printf("%d\n", ans);
    }
    return 0;
}