Python Program for Find the element that appears once

Last Updated : 22 Dec, 2021

Given an array where every element occurs three times, except one element which occurs only once. Find the element that occurs once. Expected time complexity is O(n) and O(1) extra space.
Examples :

Input: arr[] = {12, 1, 12, 3, 12, 1, 1, 2, 3, 3}
Output: 2
In the given array all element appear three times except 2 which appears once.

Input: arr[] = {10, 20, 10, 30, 10, 30, 30}
Output: 20
In the given array all element appear three times except 20 which appears once.

Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

Python3

# Python3 code to find the element that  
# appears once 
  
def getSingle(arr, n): 
    ones = 0
    twos = 0
      
    for i in range(n): 
        # one & arr[i]" gives the bits that 
        # are there in both \'ones\' and new 
        # element from arr[]. We add these 
        # bits to \'twos\' using bitwise OR 
        twos = twos | (ones & arr[i]) 
          
        # one & arr[i]" gives the bits that 
        # are there in both \'ones\' and new 
        # element from arr[]. We add these 
        # bits to \'twos\' using bitwise OR 
        ones = ones ^ arr[i] 
          
        # The common bits are those bits  
        # which appear third time. So these 
        # bits should not be there in both  
        # \'ones\' and \'twos\'. common_bit_mask 
        # contains all these bits as 0, so 
        # that the bits can be removed from 
        # \'ones\' and \'twos\' 
        common_bit_mask = ~(ones & twos) 
          
        # Remove common bits (the bits that  
        # appear third time) from \'ones\' 
        ones &= common_bit_mask 
          
        # Remove common bits (the bits that 
        # appear third time) from \'twos\' 
        twos &= common_bit_mask 
    return ones 
      
# driver code 
arr = [3, 3, 2, 3] 
n = len(arr) 
print("The element with single occurrence is ", 
        getSingle(arr, n)) 
  
# This code is contributed by "Abhishek Sharma 44" 