Brexit Gym

题目链接：Brexit

vector的使用（vector存边），巧用queue，相当于Bfs

/* */
# include <iostream>
# include <cstdio>
# include <cstring>
# include <string>
# include <memory>
# include <cstdlib>
# include <cmath>
# include <climits>
# include <cctype>
# include <cassert>
# include <utility>
# include <deque>
# include <queue>
# include <stack>
# include <vector>
# include <bitset>
# include <set>
# include <map>
# include <functional>
# include <algorithm>
using namespace std;
 
# define lson l,m,rt<<1
# define rson m+1,r,rt<<1|1
# define lowbit(x)(x&(-x))
# define lcm(a,b)(a*b/__gcd(a,b))
typedef long long ll;
const ll mod=1e9+7;
const int maxn=2e5+10;
const double eps=1e-18;
const double pi=acos(-1.0);
int n, m, c, l;
int de[maxn];
vector<int>nex[maxn];
queue<int>qu;
int flag[maxn];
 
int main()
{
    int t;
    while( ~ scanf("%d%d%d%d", &n, &m, &c, &l) )
    {
        for(int i=1; i<=n; i++ )
        {
            nex[i].clear();
            de[i]=0;
            flag[i]=0;
        }
 
        while( !qu.empty() )
            qu.pop();
        for(int i=1; i<=m; i++ )
        {
            int u, v;
            scanf("%d%d", &u, &v);
            nex[u].push_back(v);
            nex[v].push_back(u);
            de[u]++;
            de[v]++;
        }
 
        flag[l]=1;
        qu.push(l);
        while( !qu.empty() )
        {
            int cur=qu.front();
            qu.pop();
            for(int i=0; i<nex[cur].size(); i++ )
            {
                de[nex[cur][i]]--;
                if(  de[nex[cur][i]]<=nex[nex[cur][i]].size()/2 && flag[nex[cur][i]]==0 )
                {
                    flag[nex[cur][i]] = 1;//避免重复入栈
                    qu.push(nex[cur][i]);
                }
            }
        }
        if( flag[c]==1 )
            cout<<"leave"<<endl;
        else
            cout<<"stay"<<endl;
    }
    return 0;
}