2020牛客暑期多校训练营（第六场）B——Binary Vector

题目链接

题目太长了，直接找规律把~

发现

先预处理，打表，每次循环更新一下答案

#include
using namespace std;
typedef long long ll;
const int N=2e7+5;
const ll mod=1e9+7;
const ll inv2=500000004;
ll power(ll a,ll b){return b?power(a*a%mod,b/2)*(b%2?a:1)%mod:1;}
ll f[N],ans[N];
void init(){
    f[0]=1;
    ll p1=1,p2=1;
    for(ll i=1;i<=2e7;i++){
        p1=2*p1%mod;
        p2=inv2*p2%mod;
        f[i]=f[i-1]*p2%mod*(p1-1)%mod;
        ans[i]=f[i]^ans[i-1];
    }
}
int main(){
    init();
    int t,n;
    scanf("%d",&t);
    while(t--){
        scanf("%d",&n);
        printf("%lld\n",ans[n]);
    }
    return 0;
}