prim算法
cpp
int prim(){
memset(d,0x3f,sizeof d);
d[1]=0;
int res=0;
for(int i=1;i<=n;i++){
int x=-1;
for(int j=1;j<=n;j++){
if(vis[x])continue;
if(x==-1||d[j]<d[x])x=j;
}
vis[x]=1;
res+=d[x];
for(int y=1;y<=n;y++)d[y]=min(d[y],a[x][y]);
}
return res;
}