poj 3041 Asteroids(最小点覆盖)

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#define INF 0x3f3f3f3f
#define N 510

int G[N][N], vis[N], used[N];
int n;

bool Find(int u)
{
    int i;
    for(i = 1 ; i <= n ; i++)
    {
        if(!vis[i] && G[u][i])
        {
            vis[i] = 1;
            if(!used[i] || Find(used[i]))
            {
                used[i] = u;
                return true;
            }
        }
    }
    return false;
}

int main()
{
    int a, b, k, i, ans;
    while(~scanf("%d%d", &n, &k))
    {
        ans = 0;
        memset(G, 0, sizeof(G));
        while(k--)
        {
            scanf("%d%d", &a, &b);
            G[a][b] = 1;
        }
        memset(used, 0, sizeof(used));
        for(i = 1 ; i <= n ; i++)
        {
            memset(vis, 0, sizeof(vis));
            if(Find(i))
                ans++;
        }
        printf("%d\n", ans);
    }
    return 0;
}