学步园

并查集在解决图的连通性非常高效，hdu1232采用并查集，可以很快解决，代码如下：

/*
 * hdu1232.cpp
 *
 *  Created on: 2012-5-10
 *      Author: ict
 */
#include<iostream>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;

#define CLR(arr, what) memset(arr, what, sizeof(arr))
#define N 1001
int pre[N];


int Find_Set(int x) //递归+路径压缩
{
	return pre[x] == -1 ? x : (pre[x] = Find_Set(pre[x]));
}

void Make_Set(int x, int y) //无按秩合并
{
	int root1 = Find_Set(x);
	int root2 = Find_Set(y);
	if(root1 != root2)
		pre[root2] = root1;
}

int main()
{
	int i, j;
	int n, m;
	int a, b;
	int count;

	while(1)
	{
		scanf("%d", &n);
		if(!n)
			break;
		scanf("%d", &m);

		CLR(pre, -1);

		for(i = 0; i < m; i++)
		{
			scanf("%d %d", &a, &b);
			Make_Set(a, b);
		}
		count = 0;
		for(i = 1; i <= n; i++)
		{
			if(pre[i] == -1)
				count++;
		}

		printf("%d\n", count - 1);
	}

	return 0;
}