CF1731 C. Even Subarrays(思维+前缀异或和)

#include <bits/stdc++.h>

using namespace std;

#define endl "
"
#define debug cout<<"debug"<<endl
mt19937 rd(time(0));
typedef long long ll;
typedef long double ld;
typedef pair<int, int> PII;
const double eps = 1e-8;
const double PI = 3.14159265358979323;
const int N = 1e6+10, M = 2*N, mod = 1e9+7;
const int INF = 0x3f3f3f3f;

int n;

void solve()
{
    int n; cin>>n;
    vector<int> a(n), cnt(2*n);
    for(int i = 0; i<n; i++) cin>>a[i];
    ll res = 1ll*n*(n+1)/2;
    int pre = 0;
    cnt[0]++;
    // s[l~r] = s[r]^s[l-1]
    // s[i] = pre^=a[i], s[i]^(j*j) = s[x] --> s[i]^s[x] = j*j = s[x+1 ~ r], x为某个前缀x个的异或和
    // 记录所有前缀异或和的值, 再用当前的异或和 去找前缀异或和 即可遍历所有的区间的异或和
    for(int i = 0; i<n; i++)
    {
        pre ^= a[i];
        for(ll j = 0; j*j<2*n; j++)
        {
            ll x = pre^(j*j);
            if(x < 2*n) res -= cnt[x];
        }
        cnt[pre] ++;
    }
    cout<<res<<endl;

}

int main()
{
    ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
    int T;
    T = 1;
    cin>>T;
    while(T -- )
    {
        solve();
    }
    return 0;
}