poj 2599 A funny game 博弈论

思路：无向图，走过的点不能在走。dfs搞定……

再就是后继中有必败点的为必胜点！

代码如下：

 #include<iostream>
 #include<cstdio>
 #include<cmath>
 #include<algorithm>
 #include<vector>
 #include<cstring>
 using namespace std;
 int ans;
 vector<int>p[];
 bool vis[];
 int dfs(int n)
 {
     for(int i=;i<p[n].size();i++){
         if(!vis[p[n][i]]){
             vis[p[n][i]]=;
             if(!dfs(p[n][i])){
                 ans=p[n][i];
                 return ;
             }
             vis[p[n][i]]=;
         }
     }
     return ;
 }
 int main()
 {
     int n,m,a,b;
     while(scanf("%d%d",&n,&m)!=EOF){
         for(int i=;i<n;i++) p[i].clear();
         memset(vis,,sizeof(vis));
         for(int i=;i<n;i++){
             scanf("%d%d",&a,&b);
             p[a].push_back(b);
             p[b].push_back(a);
         }
         vis[m]=;
         if(dfs(m)) printf("First player wins flying to airport %d\n",ans);
         else printf("First player loses\n");
     }
     return ;
 }