poj2425--A Chess Game

题意：给定一棵有向图的树，有些节点上有石子，每次可以取一个石子向一个有向边移动，不能移动者负。

Ans：树上nim，叶子节点nim为0，父亲节点递归儿子得到sg值，答案就是每个石子所在点的sg值异或和。

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<cmath>
 #include<string>
 #include<algorithm>
 int sg[],s[],n,x,ans,m;
 int tot,go[*],first[],next[*],ru[],num;
 void insert(int x,int y){
     tot++;
     go[tot]=y;
     next[tot]=first[x];
     first[x]=tot;
 }
 int dfs(int x){
     if (s[x]!=-) return s[x];
     //if (first[x]==0) return s[x]=0;
     int ss[];
     memset(ss,,sizeof ss);
     for (int i=first[x];i;i=next[i]){
         int pur=go[i];
         ss[dfs(pur)]=;
     }
     for (int i=;i<=n+;i++)
      if (ss[i]==) return s[x]=i;
 }
 int main(){
     freopen("tx.in","r",stdin);
     while (~scanf("%d",&n)){
     memset(s,-,sizeof s);
     memset(first,,sizeof first);
     memset(ru,,sizeof ru);
     tot=;
     for (int i=;i<n;i++){
         scanf("%d",&num);
         for (int j=;j<=num;j++){
          scanf("%d",&x);
          insert(i,x);
          ru[x]++;
         }
     }
     for (int i=;i<n;i++)
      if (ru[i]==){
          s[i]=dfs(i);
      }
     while (scanf("%d",&m)&&m){
     ans=;
     for (int i=;i<=m;i++){
         scanf("%d",&x);
         ans^=s[x];
     }
     if (ans) printf("WIN\n");
     else printf("LOSE\n");
     }
     }
 }