POJ 2425 A Chess Game（有向图SG函数）题解

题意：给一个有向图，然后个m颗石头放在图上的几个点上，每次只能移动一步，如果不能移动者败

思路：dfs打表sg函数，然后求异或和

代码：

#include<queue>
#include<cstring>
#include<set>
#include<map>
#include<stack>
#include<cmath>
#include<vector>
#include<cstdio>
#include<iostream>
#include<algorithm>
#define eps 1e-9
typedef long long ll;
const int maxn = 1000 + 10;
const int seed = 131;
const ll MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f;
using namespace std;
vector<int> G[maxn];
int in[maxn], n;
int s[maxn], sg[maxn];
void dfs(int u){
    if(G[u].size() == 0){
        sg[u] = 0;
        return;
    }
    for(int i = 0; i < G[u].size(); i++){
        int v = G[u][i];
        if(sg[v] == -1)
            dfs(v);
    }
    memset(s, 0, sizeof(s));
    for(int i = 0; i < G[u].size(); i++){
        int v = G[u][i];
        s[sg[v]] = 1;
    }
    for(int i = 0; i < maxn; i++){
        if(!s[i]){
            sg[u] = i;
            return;
        }
    }
}
int main(){
    while(~scanf("%d", &n)){
        memset(in, 0, sizeof(in));
        memset(sg, -1, sizeof(sg));
        for(int i = 0; i <= n - 1; i++){
            int x, to;
            G[i].clear();
            scanf("%d", &x);
            while(x--){
                scanf("%d", &to);
                G[i].push_back(to);
                in[to]++;
            }
        }
        for(int i = 0; i <= n - 1; i++){
            if(!in[i]){
                dfs(i);
            }
        }
        int m;
        while(scanf("%d", &m) && m){
            int ans = 0, x;
            while(m--){
                scanf("%d", &x);
                ans ^= sg[x];
            }
            if(ans == 0) printf("LOSE
");
            else printf("WIN
");
        }
    }
    return 0;
}