AcWing 894. 拆分-Nim游戏

#include <cstring>
#include <iostream>
#include <algorithm>
#include <unordered_set>
using namespace std;
const int N = 110;
int n;
int f[N];
int sg(int x) {
    if (f[x] != -1) return f[x];
    unordered_set<int> S;
    for (int i = 0; i < x; i ++ )
        for (int j = 0; j <= i; j ++ )
            S.insert(sg(i) ^ sg(j));
    for (int i = 0;; i ++ )
        if (!S.count(i))
            return f[x] = i;
}
int main() {
    cin >> n;
    memset(f, -1, sizeof f);
    int res = 0;
    while (n -- ) {
        int x;
        cin >> x;
        res ^= sg(x);
    }
    if (res) puts("Yes");
    else puts("No");
    return 0;
}