G - Ice_cream's world I （并查集）

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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=1010;

int n,m;
int father[maxn];

void makeSet(){
    for(int i=0;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=0;
        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 0;
}

 

 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

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