Prim求最小生成树（朴素版稠密图）

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 510,INF = 0x3f3f3f3f;
int g[N][N],dist[N];
bool st[N];
int n,m;
int prim()
{
    
    memset(dist,0x3f,sizeof dist);
    int res=0;
    for (int i = 0; i < n; i ++ )
    {
    
        int t=-1;
        for (int j = 1; j <= n; j ++ )
            if (!st[j]&&(t==-1||dist[t]>dist[j]))
            t = j;
            if (i&&dist[t]==INF) return INF;
            if (i) res+=dist[t];
            st[t] = true;
            for (int j = 1; j <= n; j ++ )
            dist[j] = min(dist[j],g[t][j]);
    }
    return res;
}
int main()
{
    
    memset(g,0x3f,sizeof g);
    scanf("%d%d", &n, &m);
    while (m -- ){
    
        int a,b,c;
        scanf("%d%d%d", &a, &b,&c);
        g[a][b] = g[b][a]=min(g[a][b],c);
    }
    int t = prim();
    if (t==INF) puts("impossible");
    else
    printf ("%d\n",t);
    return 0;
}