How Many Tables -- 并查集

题目：

Today is Ignatius’ birthday. He invites a lot of friends. Now it’s dinner time. Ignatius wants to know how many tables he needs at least. You have to notice that not all the friends know each other, and all the friends do not want to stay with strangers.
One important rule for this problem is that if I tell you A knows B, and B knows C, that means A, B, C know each other, so they can stay in one table.
For example: If I tell you A knows B, B knows C, and D knows E, so A, B, C can stay in one table, and D, E have to stay in the other one. So Ignatius needs 2 tables at least.

Input
The input starts with an integer T(1<=T<=25) which indicate the number of test cases. Then T test cases follow. Each test case starts with two integers N and M(1<=N,M<=1000). N indicates the number of friends, the friends are marked from 1 to N. Then M lines follow. Each line consists of two integers A and B(A!=B), that means friend A and friend B know each other. There will be a blank line between two cases.

Output
For each test case, just output how many tables Ignatius needs at least. Do NOT print any blanks.

Sample Input
2
5 3
1 2
2 3
4 5

5 1
2 5

Sample Output
2
4

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题意：

给出t组测试数据，每组有一个n代表n个人和一个m代表m个关系，每个关系代表这两个人互相认识，要求我们做的是求出有多少个小团体。

分析：

并查集。

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代码如下：

#include <cstdio>#include <iostream>#include <cstring>using namespace std;int ar[50005];void init(int n){    for(int i = 0; i <= n; i++)    {        ar[i] = i;    }}int find_boss(int x){    if(ar[x] != x)        ar[x] = find_boss(ar[x]);    return ar[x];}bool same(int x, int y){    return find_boss(x) == find_boss(y);}void unite(int x, int y){    int i = find_boss(x);    int j = find_boss(y);    ar[j] = i;}int main(){    int n, m, time;    cin >> time;    while(time--)    {        cin >> n >> m;        init(n);        while(m--)        {            int a;            int b;            cin >> a >> b;            unite(a, b);        }        int cnt = 0;        for(int i = 1; i <= n; i++)        {            if(ar[i] == i)                cnt++;        }        cout << cnt << endl;    }    return 0;}

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