九度OJ 1024 畅通工程

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最小生成树----Kruskal算法

#include <stdio.h>
#include <algorithm>
using namespace std;

int Tree[101];
int findRoot(int x){
	if(Tree[x] == -1) return x;
	else{
		int tmp = findRoot(Tree[x]);
		Tree[x] = tmp;
		return tmp;
	}
}
struct Edge{
	int a , b;
	int cost;
	int operator < (const Edge &A) const{
		return cost < A.cost;
	}
}edge[101];

int main()
{
	int n , m;
	while(scanf("%d%d",&n,&m) != EOF && n != 0){
		for(int i = 1 ; i <= n ; ++i){
			scanf("%d%d%d",&edge[i].a,&edge[i].b,&edge[i].cost);
		}

		sort(edge+1,edge+ 1 + n);

		for(int i = 1 ; i <= m ;  ++i){
			Tree[i] = -1;
		}

		int ans = 0;
		for(int i = 1 ; i <= n ; i++){
			int a , b;
			a = findRoot(edge[i].a);
			b = findRoot(edge[i].b);
			if(a != b){
				Tree[a] = b;
				ans += edge[i].cost;
			}
		}
		int cnt = 0;
		for(int i = 1 ; i <= m ; i++){			//判断集合个数	
			if(Tree[i] == -1)++cnt;		
		}
		if(cnt == 1){					//最小生成树存在
			printf("%d\n",ans);
		}
		else{
			printf("?\n");
		}
	}
	return 0;
}