G - Ice_cream's world I （并查集）

点击打开链接

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.

InputIn 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. OutputOutput 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

AC代码

 #include<iostream>
 #include<cstdio>
 #include<cstring>

 using namespace std;

 const int maxn=;

 int n,m;
 int father[maxn];

 void makeSet(){
     for(int i=;i<n;i++){
         father[i]=i;
     }
 }

 int findSet(int x){
     if(x!=father[x]){
         father[x]=findSet(father[x]);
     }
     return father[x];
 }

 int main(){

     //freopen("input.txt","r",stdin);

     while(~scanf("%d%d",&n,&m)){
         makeSet();
         int ans=;
         int a,b;
         while(m--){
             scanf("%d%d",&a,&b);
             int fx=findSet(a);
             int fy=findSet(b);
             if(fx==fy)
                 ans++;
             else
                 father[fx]=fy;
         }
         printf("%d\n",ans);
     }
     return ;
 }

 做这道题快有一年了，可是现在看来还是那么的陌生，真不知道自己这一年到底学到了什么？自己是不是在虚度光阴？

这有一个并查集详解，讲得很好

点击打开链接