pku 3041 Asteroids 二分图匹配——匈牙利算法求最小点覆盖

http://poj.org/problem?id=3041

将行与列转化为左右点集，只要出现Asteroids的点（i,j）就对i j建边，然后求最小点覆盖即可。。。

#include <cstdio>
#include <cstring>
#include <iostream>
#define maxn 507
using namespace std;
int map[maxn][maxn];
int link[maxn];
bool vt[maxn];
int n,m;
bool dfs(int rpos)
{
    int i;
    for (i = 1; i <= n; ++i)
    {
        if (!vt[i] && map[rpos][i])
        {
            vt[i] = true;
            if (link[i] == -1 || dfs(link[i]))
            {
                link[i] = rpos;
                return true;
            }
        }
    }
    return false;
}
void init()
{
    int i,j;
    for (i = 0; i <= n; ++i)
    {
        link[i] = -1;
        for (j = 0; j <= n; ++j)
        map[i][j] = 0;
    }
}
int main()
{
    int i,x,y;
    cin>>n>>m;
    init();
    for (i = 0; i < m; ++i)
    {
        cin>>x>>y;
        map[x][y] = 1;
    }
    int count = 0;
    for (i = 1; i <= n; ++i)
    {
        memset(vt,false,sizeof(vt));
        if (dfs(i)) count++;
    }
    cout<<count<<endl;
    return 0;
}