AtCoder Regular Contest 078D

两边bfs，先一边找到从1到n的路径并记录下来，然后挨个标记，最后一边bfs找1能到达的点，比较一下就行了

#include<map>
#include<set>
#include<cmath>
#include<queue>
#include<stack>
#include<vector>
#include<cstdio>
#include<cassert>
#include<iomanip>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<algorithm>
#define pi acos(-1)
#define ll long long
#define mod 1000000007
#define ls l,m,rt<<1
#define rs m+1,r,rt<<1|1
#pragma comment(linker, "/STACK:1024000000,1024000000")
 
using namespace std;
 
const double g=10.0,eps=1e-4;
const int N=200000+10,maxn=500+100,inf=0x3f3f3f;
 
vector<int>v[N],p;
bool vis[N];
int pre[N],n,res;
int color[N];
void bfs(int x)
{
    memset(vis,0,sizeof vis);
    memset(pre,-1,sizeof pre);
    queue<int>q;
    q.push(x);
    vis[x]=1;
    while(!q.empty()){
        int s=q.front();
        q.pop();
        for(int i=0;i<v[s].size();i++)
        {
            if(!vis[v[s][i]])
            {
                vis[v[s][i]]=1;
                pre[v[s][i]]=s;
                q.push(v[s][i]);
                if(v[s][i]==n)return ;
            }
        }
    }
}
int bfs1(int x)
{
    memset(vis,0,sizeof vis);
    queue<int>q;
    q.push(x);
    vis[1]=1;
    int ans=0;
    while(!q.empty()){
        int s=q.front();
     //   cout<<s<<endl;
        ans++;
        q.pop();
        for(int i=0;i<v[s].size();i++)
        {
            if(color[v[s][i]]==2||vis[v[s][i]])continue;
            q.push(v[s][i]);
            vis[v[s][i]]=1;
        }
    }
    return ans;
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin>>n;
    for(int i=2;i<=n;i++)
    {
        int a,b;
        cin>>a>>b;
        v[a].push_back(b);
        v[b].push_back(a);
    }
    bfs(1);
    int ans=0;
    for(int i=pre[n];i!=1;i=pre[i])ans++;
    ans/=2;
    memset(color,0,sizeof color);
    color[1]=1,color[n]=2;
    for(int i=pre[n];i!=1;i=pre[i])
    {
        if(ans>0)ans--,color[i]=2;
        else color[i]=1;
    }
  //  for(int i=1;i<=n;i++)cout<<color[i]<<endl;
    int res=bfs1(1);
    if(res>n-res)cout<<"Fennec"<<endl;
    else cout<<"Snuke"<<endl;
    return 0;
}