E. Game of Stones
链接：
http://codeforces.com/contest/768/problem/E
题解：
状态数为 n(n+1)/2 <=x 的最大x，之后就进行异或和即可。
代码 ：
1 #include <map> 2 #include <set> 3 #include <cmath> 4 #include <queue> 5 #include <stack> 6 #include <cstdio> 7 #include <string> 8 #include <vector> 9 #include <cstring> 10 #include <iostream> 11 #include <algorithm> 12 #include <functional> 13 using namespace std; 14 #define rep(i,a,n) for (int i=a;i<=n;i++) 15 #define per(i,a,n) for (int i=n;i>=a;i--) 16 #define pb push_back 17 #define mp make_pair 18 #define all(x) (x).begin(),(x).end() 19 #define fi first 20 #define se second 21 #define SZ(x) ((int)(x).size()) 22 typedef vector<int> VI; 23 typedef long long ll; 24 typedef pair<int, int> PII; 25 const ll mod = 1000000007; 26 // head 27 28 int n, a[66]; 29 int main() 30 { 31 int st = 0, an = 0; 32 a[0] = 0; 33 rep(i, 1, 10) rep(j, 1, i + 1) a[++st] = i; 34 scanf("%d", &n); 35 while (n--){ 36 scanf("%d", &st); 37 an ^= a[st]; 38 } 39 if (an == 0) printf("YES "); 40 else printf("NO "); 41 return 0; 42 }