poj3041 Asteroids

传送门

二分图不想讲

最小点覆盖就行 每个边是一个小行星

Code:

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#define inf 2147483647
#define ms(a,b) memset(a,b,sizeof a)
#define rep(i,a,n) for(int i = a;i <= n;i++)
#define per(i,n,a) for(int i = n;i >= a;i--)
using namespace std;
typedef long long ll;
inline int read() {
    int as = 0,fu = 1;
    char c = getchar();
    while(c < '0' || c > '9') {
        if(c == '-') fu = -1;
        c = getchar();
    }
    while(c >= '0' && c <= '9') {
        as = as * 10 + c - '0';
        c = getchar();
    }
    return as * fu;
}
const int N = 200005;
//head
int n,m,ans;
int head[N],mo[N<<1],nxt[N<<1],cnt;
void add(int x,int y) {
    mo[++cnt] = y;
    nxt[cnt] = head[x];
    head[x] = cnt;
    return;
}
int match[N],vis[N];
bool dfs(int x,int tm) {
    for(int i = head[x];i;i = nxt[i]) {
        int sn = mo[i];
        if(vis[sn] == tm) continue;
        vis[sn] = tm;
        if(!match[sn] || dfs(match[sn],tm)) {
            match[sn] = x;
            return 1;
        }
    }
    return 0;
}

int main() {
    n = read(),m = read();
    rep(i,1,m) add(read(),read()+n);
    rep(i,1,n<<1) ans += dfs(i,i);
    printf("%d
",ans);
    return 0;
}