这很明显就是最大生成树= =

CODE：

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
using namespace std;
#define maxn 1010
#define maxm 20010
struct edges{
 int x,y,z;
}edge[maxm];
bool cmp(edges a,edges b){return (a.z>b.z);}
int f[maxn];
int fin(int x){if (f[x]!=x) f[x]=fin(f[x]);return f[x];}
int main(){
 int n,m;
 scanf("%d%d",&n,&m);
 for (int i=1;i<=n;i++) f[i]=i;
 for (int i=1;i<=m;i++) scanf("%d%d%d",&edge[i].x,&edge[i].y,&edge[i].z);
 sort(edge+1,edge+1+m,cmp);
 int sum=0,ans=0;
 for (int i=1;i<=m;i++){
  int x=fin(edge[i].x),y=fin(edge[i].y);
  if (x!=y) { f[x]=y;sum++;ans+=edge[i].z;if (sum==n-1) {printf("%d",ans);return 0;}}
 }
 printf("-1\n");
 return 0;
}