BZOJ 1854 【Scoi2010】 游戏

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#define File(s) freopen(s".in","r",stdin),freopen(s".out","w",stdout)
#define N 10010
#define M 1000010

using namespace std;
typedef long long llg;

int n,pip[M],vis[M],cnt;
int head[N],next[M<<1],to[M<<1],tt;

int getint(){
	int w=0;bool q=0;
	char c=getchar();
	while((c>‘9‘||c<‘0‘)&&c!=‘-‘) c=getchar();
	if(c==‘-‘) c=getchar(),q=1;
	while(c>=‘0‘&&c<=‘9‘) w=w*10+c-‘0‘,c=getchar();
	return q?-w:w;
}

void link(int x,int y){to[++tt]=y;next[tt]=head[x];head[x]=tt;}
bool dfs(int u){
	for(int i=head[u],v;i;i=next[i])
		if(vis[to[i]]!=cnt){
			v=to[i]; vis[v]=cnt;
			if(!pip[v] || dfs(pip[v])){
				pip[v]=u; return 1;
			}
		}
	return 0;
}

int main(){
	n=getint();
	for(int i=1;i<=n;i++)
		link(getint(),i),link(getint(),i);
	for(int i=1;i<=10000;i++){
		cnt++;
		if(!dfs(i)){
			printf("%d",i-1);
			return 0;
		}
	}
	printf("10000");
}