Prim算法求最小生成树

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int N=510,INF=0x3f3f3f3f;
int n,m;
int g[N][N];
int dist[N];
bool st[N];
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];
for(int j=1;j<=n;j++) dist[j]=min(dist[j],g[t][j]);
st[t]=true;
}
return res;
}
int main()
{
cin>>n>>m;
memset(g,0x3f,sizeof g);
while(m--)
{
int a,b,c;
cin>>a>>b>>c;
g[a][b]=g[b][a]=min(g[a][b],c);
}
int t=Prim();
if(t==INF) puts("impossible");
else cout<<t<<endl;
return 0;
}