title: Find The Element That Appears Once
signature: func findTheElementThatAppearsOnce(arr []int, n int) int {
test_code: package main
  
  import (
      "fmt"
      "reflect"
      "math"
      "sort"
  )
  
  // SOLUTION CODE
  // ===================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE
  // ===================================
  func validateSolution(actual int, expected int) bool {
      return reflect.DeepEqual(actual,expected)
  }
  
  func driver(arr []int, n int, expected int) string {
      if validateSolution(PLACEHOLDER_FN_NAME(arr, n),expected) {
              return "PASSED"
      }
      return "FAILED"
  
  }
  
  func main() {
  
      // Use imports to avoid undefined errors
      var _ = reflect.DeepEqual
      _ = math.Abs
      _ = sort.Sort
      result := ""
      result = driver([]int{7, 26, 26, 48, 59, 62, 66, 70, 72, 75, 76, 81, 97, 98}, 
  	7, 72)
      fmt.Printf("TEST-0...%s\n", result)
      
      result = driver([]int{-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)
      fmt.Printf("TEST-1...%s\n", result)
      
      result = driver([]int{0, 0, 1, 1}, 
  	3, 1)
      fmt.Printf("TEST-2...%s\n", result)
      
      result = driver([]int{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)
      fmt.Printf("TEST-3...%s\n", result)
      
      result = driver([]int{-98, -96, -92, -62, -52, -42, -42, -26, 4, 10, 14, 38, 64, 66, 72, 74, 82}, 
  	14, 104)
      fmt.Printf("TEST-4...%s\n", result)
      
      result = driver([]int{0, 1, 1, 1, 0, 0, 0, 1, 0, 1}, 
  	5, 0)
      fmt.Printf("TEST-5...%s\n", result)
      
      result = driver([]int{53, 63, 63}, 
  	2, 10)
      fmt.Printf("TEST-6...%s\n", result)
      
      result = driver([]int{-96, -38, -26, -46, 68, -36, 20, -18, -10, 52, 40, 94, -8, -64, 82, -22}, 
  	15, 34)
      fmt.Printf("TEST-7...%s\n", result)
      
      result = driver([]int{0, 0, 0, 0, 0, 1, 1}, 
  	3, 0)
      fmt.Printf("TEST-8...%s\n", result)
      
      result = driver([]int{99, 46, 48, 81, 27, 97, 26, 50, 77, 32, 45, 99, 46}, 
  	12, 1)
      fmt.Printf("TEST-9...%s\n", result)
      
          
  }
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;
  }