const int N = 2e5 + 10;
int n;
int a[N];
void solve() {    
    cin >> n;
    int sum = 0;
    for(int i = 1; i <= n; i ++ ) cin >> a[i], sum += a[i];

    if(sqrt(sum) * sqrt(sum) == sum) {
        cout << "YES" << endl;
    }
    else cout << "NO" << endl;
}

为什么sqrt(sum) * sqrt(sum) 可能会错 但是

    int res = sqrt(sum);
    //cout << sqrt(sum) * sqrt(sum) << endl;
    if(res * res == sum) {
        cout << "YES" << endl;
    }
    else cout << "NO" << endl;

这样写就是对的