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POJ 1611-The Suspects(并查集求秩)

2024-11-01 07:30:02   208人阅读

The Suspects
Time Limit: 1000MS Memory Limit: 20000K
Total Submissions: 23610 Accepted: 11513

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

题意：找出SARS病毒的可疑携带者，0号同学为感染者，所以与0号同学同组的人都为可疑携带者

思路：简单的并查集，找到以0为头的组，然后求出该组的秩的大小。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <iostream>
#include <algorithm>
#include <queue>
#include <set>
using namespace std;
int uset[30010];
int rank[30010];
void makeset(int n)
{
        memset(uset,0,sizeof(uset));
        for(int i=0; i<n; i++) {
                {
                        uset[i]=i;
                        rank[i]=1;
                }
        }
}
int findx(int x)
{
        if(x!=uset[x])
                uset[x]=findx(uset[x]);
        return uset[x];
}
void unionset(int x,int y)
{
        if((x=findx(x))==(y=findx(y)))
                return ;
        if(rank[x]>=rank[y]) {
                uset[y]=x;
                rank[x]=rank[x]+rank[y];
        } else {
                uset[x]=y;
                rank[y]=rank[y]+rank[x];
        }
}
int main()
{
        int n,m,k,i,j;
        int first,next;
        while(~scanf("%d %d",&n,&m)) {
                if(n==0&&m==0)
                        break;
                makeset(n);
                for(i=0; i<m; i++) {
                        scanf("%d %d",&k,&first);
                        for(j=1; j<k; j++) {
                                scanf("%d",&next);
                                unionset(first,next);
                        }
                }
                printf("%d\n",rank[uset[0]]);
        }
        return 0;
}


POJ 1611-The Suspects(并查集求秩)


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