title: Find Repetitive Element 1 N 1 2
signature: function findRepetitiveElement1N12(arr, n) {
test_code: 
  
  // SOLUTION CODE
  // ============================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE 
  // ============================================
  function convertToString(value) {
      return JSON.stringify(value, function (key, val) {
          if (val instanceof Set) {
              return Array.from(val);
          } return val;});
  }
  
  function validateSolution(actual, expected){
      return convertToString(actual)===convertToString(expected);
  }
  
  function driver(arr, n, expected){
      try{
          if (validateSolution(PLACEHOLDER_FN_NAME(arr, n),expected)){
              return "PASSED";
          }
          return "FAILED";
      } catch (error) {
        return error.name;
      }
      
  }
      
  function main(){
    let result = '';
    result = driver([2, 2, 4, 5, 5, 7, 7, 7, 8, 11, 14, 15, 18, 19, 20, 25, 25, 29, 29, 31, 32, 32, 33, 38, 42, 48, 52, 55, 60, 61, 63, 71, 74, 78, 82, 82, 84, 84, 87, 87, 88, 90, 93, 94, 94], 31, 52);
    console.log(`TEST-0...${result}`);
  
    result = driver([46, 2, 62, 60, 92, 4, 26, 66, 66, 90, 26, -14, 76, -20, -68], 8, 46);
    console.log(`TEST-1...${result}`);
  
    result = driver([0, 0, 0, 1, 1, 1, 1, 1], 4, 1);
    console.log(`TEST-2...${result}`);
  
    result = driver([87, 67, 11, 47, 64, 81, 94, 75, 58, 77, 18, 2, 85, 26, 6, 44, 55, 19, 46, 49, 5, 69, 44, 12, 42, 66, 46, 9, 26, 49, 68, 95, 6, 9, 11, 72, 5, 67], 34, 28);
    console.log(`TEST-3...${result}`);
  
    result = driver([-98, -94, -92, -82, -78, -64, -62, -58, -52, -44, -40, -38, -8, 6, 10, 20, 22, 28, 30, 30, 36, 54, 54, 58, 64, 68, 76, 78, 84, 88, 90, 94, 96], 29, -32);
    console.log(`TEST-4...${result}`);
  
    result = driver([1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1], 17, 16);
    console.log(`TEST-5...${result}`);
  
    result = driver([1, 14, 15, 15, 21, 34, 38, 39, 41, 50, 60, 74, 96, 97], 7, 25);
    console.log(`TEST-6...${result}`);
  
    result = driver([96, -12, -16, -52], 3, 103);
    console.log(`TEST-7...${result}`);
  
    result = driver([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1], 21, 21);
    console.log(`TEST-8...${result}`);
  
    result = driver([66, 21, 21, 59, 78, 8, 46, 41, 16, 32, 97, 93, 32, 86, 91, 61, 67, 61, 97, 49, 66, 35, 24, 35, 65, 45, 83], 25, 9);
    console.log(`TEST-9...${result}`);
  
    process.exit(0);
  };
  
  if (require.main === module) {
    main();
  }
source_py: def find_repetitive_element_1_n_1_2(arr, n):
      res = 0
      for i in range(0, (n - 1)):
          res = ((res ^ (i + 1)) ^ arr[i])
      res = (res ^ arr[(n - 1)])
      return res
source_cpp: int find_repetitive_element_1_n_1_2(vector<int> arr, int n) {
    int res = 0;
    for ( int i = 0;
    i < n - 1;
    i ++ ) res = res ^ ( i + 1 ) ^ arr [ i ];
    res = res ^ arr [ n - 1 ];
    return res;
  }