poj 3041 Asteroids （二分图最大匹配 == 最小点覆盖数）

/*=============================================================================
#
#      Author: liangshu - cbam 
#
#      QQ : 756029571 
#
#      School : 哈尔滨理工大学 
#
#      Last modified: 2015-08-27 16:22
#
#     Filename: C.cpp
#
#     Description: 
#        The people who are crazy enough to think they can change the world, are the ones who do ! 
=============================================================================*/
#
#include<iostream>    
#include<sstream>    
#include<algorithm>    
#include<cstdio>    
#include<string.h>    
#include<cctype>    
#include<string>    
#include<cmath>    
#include<vector>    
#include<stack>    
#include<queue>    
#include<map>    
#include<set>    
using namespace std;
int N, K;
const int INF = 505;
int from[INF],tot;
bool use[INF];
vector<int>G[INF];
bool match(int x){
    for(int i = 0; i < G[x].size(); i++){
        if(!use[G[x][i]]){
            use[G[x][i]] = 1;
            if(from[G[x][i]] == -1 || match(from[G[x][i]])){
                from[G[x][i]] = x;
                return 1;
            }
        }
    }
   return 0;
}

int hungary(){
    tot = 0;
    memset(from, 255, sizeof(from));
    for(int i = 1; i <= N; i++){
        memset(use, 0, sizeof(use));
        if(match(i))
            ++tot;
    }
    return tot;
}

int main(){
    while(scanf("%d%d",&N, &K) != EOF){
      for(int i = 0; i < K; i++){
        int a, b;
        scanf("%d%d",&a, &b);
        G[a].push_back(b);
    }
    int ans = hungary();
    cout<<ans<<endl;
    for(int i = 0; i < INF; i++){
        G[i].clear();

    }
 }
    return 0;
}
/*
 3 4
 1 1
 1 3
 3 1
 2 2
 */