poj1611(簡單並查集)

The Suspects

Time Limit: 1000MS		Memory Limit: 20000K
Total Submissions: 19335		Accepted: 9377

Description

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

Source

Asia Kaohsiung 2003

簡單的並查集的應用。

只需要將屬於同一個group內的點 unite就可以。

最後輸出和0 在同一個 group的同學數目 就可以了。

提交記錄：

1.Accepted！

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#define oo 0x3f3f3f3f
#define MAX_N 30010
#define MAX_M 510
using namespace std;
int n, m;
int par[MAX_N];
int rank[MAX_N];
void init() {
    for (int i = 0; i < n; i++) {
        par[i] = i;
        rank[i] = 0;//所有跟，纔有rank值
    }
}
int find(int x) {
    if (par[x] == x) return x;
    return par[x] = find(par[x]);//很銷魂，將par[x]修改了,提高了搜索速度
}
void unite(int x, int y) {
    x = find(x); y = find(y);//將2個結點的跟連在一起
    if (x == y) return;
    if (rank[x] < rank[y]) {
        par[x] = y;
    }
    else {
        par[y] = x;
        if (rank[x] == rank[y]) rank[x]++;
    }
}
bool same(int x, int y) {
    return (find(x) == find(y));
}
int main() {
    while (cin >> n >> m) {
        if (n == m  && n == 0) break;
        int i, j;
        int a, b;
        int num;
        init();
        for (i = 0; i < m; i++) {
            cin >> num;
            for (j = 0; j < num; j++) {
                cin >> b;
                if (j >= 1) {
                    if (!same(a, b)) {
                        unite(a, b);
                    }
                }
                a = b;
            }
        }
        int sars = find(0);
        int result = 0;
        for (i = 0; i < n; i++) {
            if (sars == find(i)) result ++;
        }
        cout << result << endl;
    }
    return 0;
}