title: Find The Missing Number 2
signature: function find_the_missing_number_2(a, n)
test_code: using Printf
  
  # SOLUTION CODE
  # ============================================
  PLACEHOLDER_CODE_BODY
  
  # TESTING CODE 
  # ============================================
  function validate_solution(actual, expected)
      return actual == expected
  end
  
  function driver(a, n, expected)
      try
  
          if validate_solution(PLACEHOLDER_FN_NAME(a, n), expected)
              return "PASSED";
          end
          return "FAILED";
      catch exception_obj
          return string(Base.typename(typeof(exception_obj)).wrapper);
      end
  end
  
  function main()
      
      result = driver([2, 5, 7, 8, 10, 14, 27, 32, 51, 52, 57, 58, 65, 68, 68, 72, 73, 73, 83, 92, 98], 12, 50);
      @printf("TEST-0...%s\n",result);
      
      result = driver([-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);
      @printf("TEST-1...%s\n",result);
      
      result = driver([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);
      @printf("TEST-2...%s\n",result);
      
      result = driver([69, 59, 22, 33, 69, 28, 11, 34, 72, 88, 16, 30, 69, 89, 43, 4, 65, 85, 27], 13, 109);
      @printf("TEST-3...%s\n",result);
      
      result = driver([-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);
      @printf("TEST-4...%s\n",result);
      
      result = driver([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);
      @printf("TEST-5...%s\n",result);
      
      result = driver([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);
      @printf("TEST-6...%s\n",result);
      
      result = driver([62, -66, 60, -92, 46, 6, -52, 48, 72, -64, 34, 20, 50, 70, -34, 20, -70, 14, -44, 66, -70], 17, 101);
      @printf("TEST-7...%s\n",result);
      
      result = driver([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);
      @printf("TEST-8...%s\n",result);
      
      result = driver([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);
      @printf("TEST-9...%s\n",result);
      
  end
  
  main()
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 );
  }