Asteroids

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

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;
const int MAXN=555;
int n,k;
bool use[MAXN];
int from[MAXN],ans;
vector<int>g[MAXN];
bool match(int x)
{
    for(int i=0;i<g[x].size();i++)
    {
        if(!use[g[x][i]]){
            use[g[x][i]]=true;
            if(from[g[x][i]]==-1||match(from[g[x][i]])){
                from[g[x][i]]=x;
                return true;
            }
        }
    }
    return false;
}

int hun()
{

    ans=0;
    memset(from,255,sizeof(from));
    for(int i=1; i<=n; i++)
    {
        memset(use,false,sizeof(use));
        if(match(i))
        ans++;
    }
    return ans;
}
int main()
{
    int a,b;
   while(scanf("%d%d",&n,&k)!=EOF){
    for(int i=1;i<=k;i++)
    {
        scanf("%d%d",&a,&b);
        g[a].push_back(b);
    }
    printf("%d\n",hun());
   }
    return 0;
}

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;
const int MAXN=520;
int n,k;
bool use[MAXN];
int match[MAXN],ans;
int g[MAXN][MAXN];
bool dfs(int x)
{
    for(int i=1;i<=n;i++)
    {
        if(!use[i]&&g[x][i]){
            use[i]=true;
            if(match[i]==-1||dfs(match[i])){
                match[i]=x;
                return true;
            }
        }
    }
    return false;
}

int hun()
{

    ans=0;
    memset(match,-1,sizeof(match));
    for(int i=1; i<=n; i++)
    {
        memset(use,false,sizeof(use));
        if(dfs(i))
        ans++;
    }
    return ans;
}
int main()
{
    int a,b;
    while(scanf("%d%d",&n,&k)!=EOF)
    {
        memset(g,0,sizeof(g));
        for(int i=1; i<=k; i++)
        {
            scanf("%d%d",&a,&b);
             g[a][b]=1;
        }
        printf("%d\n",hun());
    }
    return 0;
}