title: Find The Element That Appears Once
signature: fun findTheElementThatAppearsOnce(arr: ArrayList<Int>, n: Int): Int {
test_code: package main
  
  import kotlin.text.*
  import kotlin.math.*
  
  
  // SOLUTION CODE
  // ===================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE
  // ===================================
  fun validateSolution(actual:Int, expected:Int):Boolean{
    return actual.equals(expected)
  }
  fun driver(arr: ArrayList<Int>, n: Int, expected:Int):String {
      try{
        if (validateSolution(PLACEHOLDER_FN_NAME(arr, n), expected)) {
                return "PASSED"
        }
        return "FAILED"
      } catch (e: Exception){
        return e::class.simpleName as String
      }
  
  }
  
  fun main() {
      var result: String = ""
      result = driver(arrayListOf(7, 26, 26, 48, 59, 62, 66, 70, 72, 75, 76, 81, 97, 98), 7, 72)
      println("TEST-0...${result}")
      
      result = driver(arrayListOf(-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)
      println("TEST-1...${result}")
      
      result = driver(arrayListOf(0, 0, 1, 1), 3, 1)
      println("TEST-2...${result}")
      
      result = driver(arrayListOf(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)
      println("TEST-3...${result}")
      
      result = driver(arrayListOf(-98, -96, -92, -62, -52, -42, -42, -26, 4, 10, 14, 38, 64, 66, 72, 74, 82), 14, 104)
      println("TEST-4...${result}")
      
      result = driver(arrayListOf(0, 1, 1, 1, 0, 0, 0, 1, 0, 1), 5, 0)
      println("TEST-5...${result}")
      
      result = driver(arrayListOf(53, 63, 63), 2, 10)
      println("TEST-6...${result}")
      
      result = driver(arrayListOf(-96, -38, -26, -46, 68, -36, 20, -18, -10, 52, 40, 94, -8, -64, 82, -22), 15, 34)
      println("TEST-7...${result}")
      
      result = driver(arrayListOf(0, 0, 0, 0, 0, 1, 1), 3, 0)
      println("TEST-8...${result}")
      
      result = driver(arrayListOf(99, 46, 48, 81, 27, 97, 26, 50, 77, 32, 45, 99, 46), 12, 1)
      println("TEST-9...${result}")
      
          
  }
  
  main()
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;
  }