title: Find The Missing Number 2
signature: def findTheMissingNumber2(a: 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(a: List[Int], n: Int, expected: Int): String = {
      try {
          if (validateSolution(PLACEHOLDER_FN_NAME(a, n),expected)) {
              "PASSED"
          } else{
              "FAILED"
          }
      }catch{
          case e: Exception => {e.getClass.getName}
      }
  
  }
  object QuestionEvaluator extends App {
  
      println(s"TEST-0...${driver(
        List(2, 5, 7, 8, 10, 14, 27, 32, 51, 52, 57, 58, 65, 68, 68, 72, 73, 73, 83, 92, 98), 12, 
        50    
      )}")   
  
  
      println(s"TEST-1...${driver(
        List(-60, -48, 38, -78, 88, 86, -4, -94, 16, -64, 32, 88, 58, -78, -16, 48, 38, 30, 66, -60, 20, 40, -28, -64, -48, -86, -80, -8, -58, 52, 80, -32, 46, -4, -70, 76, -4, 78, -64, 38, -40), 28, 
        -91    
      )}")   
  
  
      println(s"TEST-2...${driver(
        List(0, 0, 0, 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, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1), 38, 
        1    
      )}")   
  
  
      println(s"TEST-3...${driver(
        List(69, 59, 22, 33, 69, 28, 11, 34, 72, 88, 16, 30, 69, 89, 43, 4, 65, 85, 27), 13, 
        109    
      )}")   
  
  
      println(s"TEST-4...${driver(
        List(-98, -98, -92, -88, -88, -82, -74, -70, -68, -60, -60, -48, -38, -34, -34, -24, 14, 38, 50, 58, 62, 64, 64, 68, 76, 78, 78, 86, 88, 90, 92, 98, 98), 23, 
        94    
      )}")   
  
  
      println(s"TEST-5...${driver(
        List(0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 0), 41, 
        42    
      )}")   
  
  
      println(s"TEST-6...${driver(
        List(1, 9, 12, 12, 24, 25, 33, 33, 36, 39, 46, 48, 48, 52, 52, 53, 57, 69, 71, 72, 75, 76, 78, 80, 82, 86, 89, 91, 94, 95, 96, 97, 98, 99), 30, 
        124    
      )}")   
  
  
      println(s"TEST-7...${driver(
        List(62, -66, 60, -92, 46, 6, -52, 48, 72, -64, 34, 20, 50, 70, -34, 20, -70, 14, -44, 66, -70), 17, 
        101    
      )}")   
  
  
      println(s"TEST-8...${driver(
        List(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, 1, 1, 1, 1, 1, 1, 1, 1), 30, 
        0    
      )}")   
  
  
      println(s"TEST-9...${driver(
        List(33, 10, 6, 71, 18, 22, 15, 57, 56, 63, 35, 93, 31, 43, 98, 99, 62, 39, 44, 86, 78, 95, 6, 76, 71), 12, 
        32    
      )}")   
  
  }
  
source_py: def find_the_missing_number_2(a, n):
      x1 = a[0]
      x2 = 1
      for i in range(1, n):
          x1 = (x1 ^ a[i])
      for i in range(2, (n + 2)):
          x2 = (x2 ^ i)
      return (x1 ^ x2)
source_cpp: int find_the_missing_number_2(vector<int> a, int n) {
    int x1 = a [ 0 ];
    int x2 = 1;
    for ( int i = 1;
    i < n;
    i ++ ) x1 = x1 ^ a [ i ];
    for ( int i = 2;
    i <= n + 1;
    i ++ ) x2 = x2 ^ i;
    return ( x1 ^ x2 );
  }