The Suspects -- 并查集

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概述

题目：

Severe acute respiratory syndrome (SARS), an atypical pneumonia of unknown aetiology, was recognized as a global threat in mid-March 2003. To minimize transmission to others, the best strategy is to separate the suspects from others.
In the Not-Spreading-Your-Sickness University (NSYSU), there are many student groups. Students in the same group intercommunicate with each other frequently, and a student may join several groups. To prevent the possible transmissions of SARS, the NSYSU collects the member lists of all student groups, and makes the following rule in their standard operation procedure (SOP).
Once a member in a group is a suspect, all members in the group are suspects.
However, they find that it is not easy to identify all the suspects when a student is recognized as a suspect. Your job is to write a program which finds all the suspects.

Input
The input file contains several cases. Each test case begins with two integers n and m in a line, where n is the number of students, and m is the number of groups. You may assume that 0 < n <= 30000 and 0 <= m <= 500. Every student is numbered by a unique integer between 0 and n−1, and initially student 0 is recognized as a suspect in all the cases. This line is followed by m member lists of the groups, one line per group. Each line begins with an integer k by itself representing the number of members in the group. Following the number of members, there are k integers representing the students in this group. All the integers in a line are separated by at least one space.
A case with n = 0 and m = 0 indicates the end of the input, and need not be processed.

Output
For each case, output the number of suspects in one line.

Sample Input
100 4
2 1 2
5 10 13 11 12 14
2 0 1
2 99 2
200 2
1 5
5 1 2 3 4 5
1 0
0 0

Sample Output
4
1
1

题意：

给出n和m代表n个人和m组数据，每组数据内的所有编号代表这些人是在同一组，如果其中有一个人患病，那么其他人也都患病，每次测试数据都默认0号一定会患病，我们需要输出的是患病的总人数，当n和m都为0的时候结束输入。

思路：

并查集标准题型。

代码如下：

#include <cstdio>
#include <string>
#include <iostream>
using namespace std;

int ar[30005];

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];
}

void unite(int x, int y)
{
    int i = find_boss(x);
    int j = find_boss(y);
    int mx = max(i ,j);
    int mn = min(i, j);
    ar[mx] = mn;
}

bool same(int x, int y)
{
    return find_boss(x) == find_boss(y);
}

int main()
{
    int n, m;
    while(cin >> n >> m && n + m > 0)
    {
        init(n);
        while(m--)
        {
            int num;
            cin >> num;
            int a;
            cin >> a;
            for(int i = 0; i < num - 1; i++)
            {
                int b;
                cin >> b;
                unite(a, b);
            }
        }
        int cnt = 0;
        for(int i = 0; i < n; i++)
        {
            if(find_boss(i) == 0)
                cnt++;
        }
        cout << cnt << endl;
    }
    return 0;
}