p106 畅通工程 同心集的数目-1就是需要建立的桥的数目

#include<stdio.h>

using namespace std;

int Tree[1005];

int root1(int x)
{
	if(Tree[x]==-1)return x;
	else
	{
		int tmp = root1(Tree[x]);
		Tree[x] = tmp;
		return tmp;
	}
}

int root(int x)
{
	int ret;
	int tmp = x;
	while(Tree[x]!=-1)
	{
		x = Tree[x];
	}
	ret = x;
    x = tmp;
	while(Tree[x]!=-1)//这个不能写成ret，否则出错！我真的不知道是为啥。。。
	{
        int t = Tree[x];
		Tree[x] = ret;
        x = t;
	}
	return ret;
}

int  main()
{
	int n,m;
	while(scanf("%d",&n)!=EOF)
	{
		if(n==0)break;
		scanf("%d",&m);
		for(int i=1;i<=n;i++)Tree[i]=-1;
		while(m--)
		{
			int a,b;
			scanf("%d %d",&a,&b);
			a = root(a);
			b = root(b);
			if(a!=b)Tree[a]=b;
		}
		int ans = 0;
		for(int i=1;i<=n;i++)
		{
			if(Tree[i]==-1)ans++;
		}
		printf("%d",ans-1);
	}
	return 0;
 }