http://acm.hdu.edu.cn/showproblem.php?pid=1213

并查集

#include<stdio.h>
#include<iostream>
#include<math.h>
#include<stdlib.h>
#include<ctype.h>
#include<algorithm>
#include<vector>
#include<string.h>
#include<queue>
#include<stack>
#include<set>
#include<map>
#include<sstream>
#include<time.h>
#include<utility> 
#include<malloc.h> 
#include<stdexcept>

using namespace std;

int n, m, t;
int p[10000];
int b[10000];

int find(int x)
{
	if (x == p[x])
		return x;
	else
		return find(p[x]);
}

int fa, fb;
void un(int x, int y)
{
	fa = find(p[x]);
	fb = find(p[y]);
	if (fa != fb)
	{
		if (fa>fb)
			p[fa] = fb;
		else
			p[fb] = fa;
	}
}

int main()
{
	scanf("%d",&t);
	while (t--)
	{
		scanf("%d%d", &n, &m);
		for (int i = 1; i <= n; i++)
			p[i] = i;

		int sum = 0;

		int a, b;
		for (int i = 1; i <= m; i++)
		{
			scanf("%d%d", &a, &b);
			un(a, b);
		}

		for (int i = 1; i <= n; i++)
		{
			if (p[i] == i)
				sum++;
		}
		printf("%d\n", sum);
	}
	return 0;
}

hdu-1213 how many tables