最小生成树
使用kruskal算法求解

#include<bits/stdc++.h>
using namespace std;
const int maxn=3005;
int n,m,ans;
struct node{
	int u,v,cost;
}E[maxn];
bool cmp(node a, node b){
	return a.cost < b.cost;
}
int father[maxn];
void init(){
	for(int i=1;i<=n;i++){
		father[i]=i;
	}
}
int findFather(int x){
	if(x==father[x]) return x;
	else {
		int tmp = findFather(father[x]);
		father[x] = tmp;
		return tmp;
	}
}
void kruskal(){
	int sum=0,k=0;
	init();	
	for(int i=0;i<m;i++){
		int faA = findFather(E[i].u);
		int faB = findFather(E[i].v);
		if(faA != faB){
			father[faA]=faB;
			k++;
			sum+=E[i].cost;
		}
	}
	if(k!=n-1) ans=-1;
	else ans = sum;
}
int main(){
	scanf("%d%d",&n,&m);
	for(int i=0;i<m;i++){
		scanf("%d%d%d",&E[i].u,&E[i].v,&E[i].cost);
	}
	sort(E,E+m,cmp);
	kruskal();
	printf("%d\n",ans);
	return 0;
}