HDU 1863 畅通工程

畅通工程系列题目

用Krustral算法就可以过

#include<iostream>
#include<cstdio>
#include<cstring>
#include<functional>
#include<algorithm>
#include<cstdlib>
using namespace std;
struct node
{
	int from,to;
	int cost;
}e[10005];
int fa[105];
int cmp(struct node a,struct node b){return a.cost<b.cost;}
int n,m,sum,cnt,i;
void init()
{
	sum=0;cnt=0;
	for(i=1;i<=m;i++)
		fa[i]=i;
}
int getfa(int x)
{
	if(x==fa[x])
		return x;
	else
		return fa[x]=getfa(fa[x]);
}
int  merge(int u,int v)
{
	int t1,t2;
	t2=getfa(u);
	t1=getfa(v);
	if(t1!=t2)
	{
		fa[t1]=t2;
		return 1;
	}
	return 0;
}
int main()
{
	while(scanf("%d%d",&n,&m),n)
	{
		init();
		for(i=1;i<=n;i++)
			scanf("%d%d%d",&e[i].from,&e[i].to,&e[i].cost);
		sort(e+1,e+n+1,cmp);
		for(i=1;i<=n;i++)
		{
			if(merge(e[i].from,e[i].to))
				cnt++,sum+=e[i].cost;
		}
		//printf("cnt=%d sum=%d\n",cnt,sum);
		if(cnt==m-1)
			printf("%d\n",sum);
		else
			printf("?\n");

	}
}