1004: 惠民工程

使用kruskal写最小生成树

#include <bits/stdc++.h>
using namespace std;
const int M=105;
const int N=5005;
struct node{
	int s;
	int t;
	int w;
	bool operator<(const node& a)const{
		return w>a.w;    //小根堆 
	}
};

int fa[M];
int find(int i){
	if(fa[i]==i){
		return i;
	}
	else fa[i]=find(fa[i]);
	return  fa[i];
}
int m,n;
int n2;
int main(){
	while(scanf("%d%d",&m,&n2)!=EOF){		//m个城市，n个管道 
		priority_queue<node> que;
		memset(fa,0,sizeof(fa));
		if(n2>m*(m-1)/2){
			n=m*(m-1)/2;
		}		
		else n=n2;				//题目给的n2管道数可能很多 
		for(int i=1;i<=n;i++){
			int s,t,w;
			scanf("%d%d%d",&s,&t,&w);
			que.push({s,t,w});
			fa[s]=s;
			fa[t]=t;
		}
		if(n<n2){
			for(int i=n+1;i<=n2;i++){
				int s,t,w;
				scanf("%d%d%d",&s,&t,&w);
			}
		}
		int cnt=0;
		long long sum=0;
		while(cnt<=m-1&&!que.empty()){
			node now=que.top();
			que.pop();
			if(find(now.s)!=find(now.t)){
				fa[fa[now.s]]=fa[now.t];
				cnt++;
				sum=sum+now.w;
			}
		}
		if(cnt==m-1){
			printf("%lld\n",sum);
		}
		else 
			printf("?\n");
	}
	return 0;
}