HDOJ 2120 并查集

并查集的应用，用来查找被分割的区域个数。

即当两个节点值相同时说明已经为了一个圈，否则不可能，此时区域个数加1.

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 using namespace std;
 const int maxn=;
 int n,m;
 int root[maxn];

 int find(int a){
     while(root[a]!=a){
         a=root[a];
     }
     return a;
 }

 int main(){
     while(EOF != scanf("%d%d",&n,&m)){
         for(int i=;i<n;i++){
             root[i]=i;
         }
         int ans = ;
         int a,b;
         while(m--){
             scanf("%d%d",&a,&b);
             int ra=find(a);
             int rb=find(b);
             if(ra == rb)
                 ans++;
             else
                 root[ra]=rb;//epual to Join
             //printf("%d %d %d\n",ra,rb,ans);
         }
         printf("%d\n",ans);
     }
     return ;
 }

Ice_cream's world I

Time Limit : 3000/1000ms (Java/Other)   Memory Limit : 32768/32768K (Java/Other)

Total Submission(s) : 3   Accepted Submission(s) : 2

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Problem Description

ice_cream's world is a rich country, it has many fertile lands. Today, the queen of ice_cream wants award land to diligent ACMers. So there are some watchtowers are set up, and wall between watchtowers be build, in order to partition the ice_cream’s world. But how many ACMers at most can be awarded by the queen is a big problem. One wall-surrounded land must be given to only one ACMer and no walls are crossed, if you can help the queen solve this problem, you will be get a land.

Input

In the case, first two integers N, M (N<=1000, M<=10000) is represent the number of watchtower and the number of wall. The watchtower numbered from 0 to N-1. Next following M lines, every line contain two integers A, B mean between A and B has a wall(A and B are distinct). Terminate by end of file.

Output

Output the maximum number of ACMers who will be awarded.
One answer one line.

Sample Input

8 10
0 1
1 2
1 3
2 4
3 4
0 5
5 6
6 7
3 6
4 7

Sample Output

3