title: Find Repetitive Element 1 N 1 2
signature: def findRepetitiveElement1N12(arr: List[Int], n: Int) = {
test_code: import scala.collection.mutable.HashMap
  import scala.collection.immutable.HashSet
  
  
  // SOLUTION CODE
  // ============================================
  PLACEHOLDER_CODE_BODY
  
  
  // TESTING CODE 
  // ============================================
  def validateSolution(actual: Int , expected: Int): Boolean = {
      actual.toString == expected.toString
  }
  
  def driver(arr: List[Int], n: Int, expected: Int): String = {
      try {
          if (validateSolution(PLACEHOLDER_FN_NAME(arr, n),expected)) {
              "PASSED"
          } else{
              "FAILED"
          }
      }catch{
          case e: Exception => {e.getClass.getName}
      }
  
  }
  object QuestionEvaluator extends App {
  
      println(s"TEST-0...${driver(
        List(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    
      )}")   
  
  
      println(s"TEST-1...${driver(
        List(46, 2, 62, 60, 92, 4, 26, 66, 66, 90, 26, -14, 76, -20, -68), 8, 
        46    
      )}")   
  
  
      println(s"TEST-2...${driver(
        List(0, 0, 0, 1, 1, 1, 1, 1), 4, 
        1    
      )}")   
  
  
      println(s"TEST-3...${driver(
        List(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    
      )}")   
  
  
      println(s"TEST-4...${driver(
        List(-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    
      )}")   
  
  
      println(s"TEST-5...${driver(
        List(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    
      )}")   
  
  
      println(s"TEST-6...${driver(
        List(1, 14, 15, 15, 21, 34, 38, 39, 41, 50, 60, 74, 96, 97), 7, 
        25    
      )}")   
  
  
      println(s"TEST-7...${driver(
        List(96, -12, -16, -52), 3, 
        103    
      )}")   
  
  
      println(s"TEST-8...${driver(
        List(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    
      )}")   
  
  
      println(s"TEST-9...${driver(
        List(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    
      )}")   
  
  }
  
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;
  }