title: Find The Element That Appears Once
signature: findTheElementThatAppearsOnce :: [Integer] -> Integer -> Integer
  findTheElementThatAppearsOnce arr n = 
test_code: import Text.Printf
  import Control.Exception (catch, SomeException)
  import Data.Typeable
  import qualified Data.List as List
  import qualified Data.Map as Map
  import qualified Data.Set as Set
  
  -- SOLUTION CODE
  -- ============================================
  
  PLACEHOLDER_CODE_BODY
  
  -- TESTING CODE 
  -- ============================================
  validateSolution :: Integer -> Integer -> Bool
  validateSolution actual expected = do
      actual == expected
  
  
  driver :: [Integer] -> Integer -> Integer -> String
  driver arr n expected = do
      if (validateSolution (PLACEHOLDER_FN_NAME arr n) expected)
          then "PASSED"
      else "FAILED"
  
  main = do
      printf "TEST-0...%s\n" (driver ([7, 26, 26, 48, 59, 62, 66, 70, 72, 75, 76, 81, 97, 98]) (7) (72) )
  
      printf "TEST-1...%s\n" (driver ([-42, -48, -64, -74, 56, -34, 20, 16, 34, -84, 86, 38, 56, -86, 30, -74, -96, 96, 12, 10, -46, 10, -36, 38, 34, -46, -20, 14, 12, 62, -54, 20, -82, 24, 96]) (27) (-28) )
  
      printf "TEST-2...%s\n" (driver ([0, 0, 1, 1]) (3) (1) )
  
      printf "TEST-3...%s\n" (driver ([68, 91, 61, 6, 32, 47, 76, 69, 44, 71, 29, 79, 74, 33, 44, 33, 45, 75, 43, 82, 83, 81, 95, 16, 86, 33, 69, 61, 73, 21, 54, 17, 98, 62, 14, 72, 80, 31, 56, 82, 14, 48, 76]) (38) (25) )
  
      printf "TEST-4...%s\n" (driver ([-98, -96, -92, -62, -52, -42, -42, -26, 4, 10, 14, 38, 64, 66, 72, 74, 82]) (14) (104) )
  
      printf "TEST-5...%s\n" (driver ([0, 1, 1, 1, 0, 0, 0, 1, 0, 1]) (5) (0) )
  
      printf "TEST-6...%s\n" (driver ([53, 63, 63]) (2) (10) )
  
      printf "TEST-7...%s\n" (driver ([-96, -38, -26, -46, 68, -36, 20, -18, -10, 52, 40, 94, -8, -64, 82, -22]) (15) (34) )
  
      printf "TEST-8...%s\n" (driver ([0, 0, 0, 0, 0, 1, 1]) (3) (0) )
  
      printf "TEST-9...%s\n" (driver ([99, 46, 48, 81, 27, 97, 26, 50, 77, 32, 45, 99, 46]) (12) (1) )
  
source_py: def find_the_element_that_appears_once(arr, n):
      ones = 0
      twos = 0
      for i in range(n):
          twos = (twos | (ones & arr[i]))
          ones = (ones ^ arr[i])
          common_bit_mask = (~ (ones & twos))
          ones &= common_bit_mask
          twos &= common_bit_mask
      return ones
source_cpp: int find_the_element_that_appears_once(vector<int> arr, int n) {
    int ones = 0, twos = 0;
    int common_bit_mask;
    for ( int i = 0;
    i < n;
    i ++ ) {
      twos = twos | ( ones & arr [ i ] );
      ones = ones ^ arr [ i ];
      common_bit_mask = ~ ( ones & twos );
      ones &= common_bit_mask;
      twos &= common_bit_mask;
    }
    return ones;
  }