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>
  #pragma GCC optimize("Ofast,03")
  #pragma GCC target( \
      "fma,sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
  #pragma GCC optimize("unroll-loops")
  using namespace std;
  using namespace std::chrono;
  bool yes(string s) {
    long long int n = s.size();
    for (long long int i = 0; i < n / 2; i++)
      if (s[i] != s[n / 2 + i]) return false;
    return true;
  }
  int32_t main() {
    auto start1 = high_resolution_clock::now();
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    long long int t;
    cin >> t;
    long long int tc = t;
    while (t--) {
      string s;
      cin >> s;
      if (yes(s) and s.size() % 2 == 0)
        cout << "YES\n";
      else
        cout << "NO\n";
    }
    auto stop1 = high_resolution_clock::now();
    auto duration = duration_cast<microseconds>(stop1 - start1);
    long long int tm = (double)duration.count() / 1000;
    cerr << "Time: " << tm << " ms" << endl;
    return 0;
  }
  