Poj2395--Out of Hay(最小生成树)

#include <cstdio>
#include <cstring>
#define N 2001
const int INF = 0x3f3f3f3f;
int dis[N], vis[N], map[N][N];
int n, m, maxlen;
void Prime()
{
    memset(vis, 0, sizeof(vis));
    for(int i = 1; i <= n; i++)
        dis[i] = map[1][i];
    vis[1] = 1; 
    for(int i = 1; i < n; i++){
        int temp, min = INF;
        for(int j = 1; j <= n; j++)
            if(!vis[j] && dis[j] < min){
                temp = j;
                min = dis[j];
            }
        if(min==INF)
            return;
        vis[temp] = 1;
        if(dis[temp] > maxlen)
            maxlen = dis[temp];
        for(int j = 1; j <= n; j++)
            if(!vis[j] && dis[j] > map[temp][j])
                dis[j] = map[temp][j];
    }
}
int main()
{
    while(scanf("%d%d", &n, &m) != EOF)
    {
        maxlen = -1;
        for(int i = 1; i <= n; i++)
            for(int j = 1; j <= n; j++)
                map[i][j] = -1;
        for(int i = 0; i < m; i++)
        {
            int a, b, c;
            scanf("%d%d%d", &a, &b, &c);
            if(map[a][b] == -1 || map[a][b] > c)
                map[a][b] = map[b][a]=c;
        }
        for(int i = 1; i <= n; i++)
            for(int j = 1; j <= n; j++)
                if(map[i][j] == -1)
                    map[i][j] = INF;
        Prime();
        printf("%d\n", maxlen);
    }    
    return 0;
}