description: A string is called square if it is some string written twice in a row. For example, the strings "aa", "abcabc", "abab" and "baabaa" are square. But the strings "aaa", "abaaab" and "abcdabc" are not square.
  
  For a given string s determine if it is square.
  
  Input
  
  The first line of input data contains an integer t (1 ≤ t ≤ 100) —the number of test cases.
  
  This is followed by t lines, each containing a description of one test case. The given strings consist only of lowercase Latin letters and have lengths between 1 and 100 inclusive.
  
  Output
  
  For each test case, output on a separate line:
  
    * YES if the string in the corresponding test case is square, 
    * NO otherwise. 
  
  
  
  You can output YES and NO in any case (for example, strings yEs, yes, Yes and YES will be recognized as a positive response).
  
  Example
  
  Input
  
  
  10
  a
  aa
  aaa
  aaaa
  abab
  abcabc
  abacaba
  xxyy
  xyyx
  xyxy
  
  
  Output
  
  
  NO
  YES
  NO
  YES
  YES
  YES
  NO
  NO
  NO
  YES
solution: #include <bits/stdc++.h>
  using namespace std;
  long long int gcd(long long int a, long long int b) {
    return b == 0 ? a : gcd(b, a % b);
  }
  long long int lcm(long long int a, long long int b) {
    return (a / gcd(a, b)) * b;
  }
  bool flip(int i, int j, vector<vector<int>> &dp) {
    if (i == 0) return false;
    if (dp[i][j] != -1) return dp[i][j];
    bool answer = false;
    if (i >= 1) answer |= !flip(i - 1, !j, dp);
    if (i >= 2) answer |= !flip(i - 2, !j, dp);
    return dp[i][j] = answer;
  }
  int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    ;
    long long int t;
    cin >> t;
    while (t--) {
      string str;
      cin >> str;
      if (str.size() % 2 != 0) {
        cout << "NO"
             << "\n";
        continue;
      }
      long long int n = str.size();
      long long int i = 0, j = n / 2;
      bool flag = false;
      while (i < n / 2 && j < n) {
        if (str[i] != str[j]) {
          flag = true;
          break;
        }
        i++;
        j++;
      }
      if (flag)
        cout << "NO";
      else
        cout << "YES";
      cout << "\n";
    }
    return 0;
  }
  