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: 
  import java.io.BufferedReader;
  import java.io.FileNotFoundException;
  import java.io.FileReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.math.BigInteger;
  import java.util.ArrayList;
  import java.util.HashSet;
  
  
  
  public class Ej1 {
      private static int gcd(int a, int b) {
          BigInteger b1 = BigInteger.valueOf(a);
          BigInteger b2 = BigInteger.valueOf(b);
          BigInteger gcd = b1.gcd(b2);
          return gcd.intValue();
      }
      static class Par{
          long x;
          long y;
  
          public Par(long x, long y) {
              this.x = x;
              this.y = y;
          }
          
      }
      public static void main(String[] args) throws FileNotFoundException, IOException {
          BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
          //BufferedReader stdin = new BufferedReader((new FileReader("/home/samuel/x.txt")));
          
          
          
          
          String line = stdin.readLine();
          long tot = Long.parseLong(line);
          
          for (long i = 0; i < tot; i++) {
              //System.out.println("caso "+i);
              line = stdin.readLine();
              
              /*String[] sp = line.split(" ");
              long w = Long.parseLong(sp[0]);
              long h = Long.parseLong(sp[1]);*/
              
              
              if (line.length()%2==1){
                  System.out.println("NO");
              }
              else
              {
                  String s1 = line.substring(0,line.length()/2);
                  String s2 = line.substring(line.length()/2);
                  //System.out.println(line +" >> " + s1 + " : " + s2);
                  if (s1.equals(s2)){
                      System.out.println("YES");
                  }
                  else{
                      System.out.println("NO");
                  }
              }
              
          }
          
      }
  }
  