title: Find Repetitive Element 1 N 1 2
signature: findRepetitiveElement1N12(arr, n) {
test_code: import 'dart:convert';
  
  // SOLUTION CODE
  // ============================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE 
  // ============================================
  bool validateSolution(int actual, int expected){
      return actual.toString() == expected.toString();
  }
  
  String driver(arr, n, int expected){
      try
      {
          if (validateSolution(PLACEHOLDER_FN_NAME(arr, n), expected)){
              return "PASSED";
          }
          return "FAILED";
      }catch(exception_object){
          return exception_object.runtimeType.toString();
      }
  }
  
  int main() {
  
      print("TEST-0...${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)
      }");
  
      print("TEST-1...${driver(
          [46, 2, 62, 60, 92, 4, 26, 66, 66, 90, 26, -14, 76, -20, -68], 8, 
          46)
      }");
  
      print("TEST-2...${driver(
          [0, 0, 0, 1, 1, 1, 1, 1], 4, 
          1)
      }");
  
      print("TEST-3...${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)
      }");
  
      print("TEST-4...${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)
      }");
  
      print("TEST-5...${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)
      }");
  
      print("TEST-6...${driver(
          [1, 14, 15, 15, 21, 34, 38, 39, 41, 50, 60, 74, 96, 97], 7, 
          25)
      }");
  
      print("TEST-7...${driver(
          [96, -12, -16, -52], 3, 
          103)
      }");
  
      print("TEST-8...${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)
      }");
  
      print("TEST-9...${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)
      }");
  
      return 0;
  }
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;
  }