Java 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.

Java

//JAVA code to find the element 
//that occur only once 
  
class GFG 
{ 
    // Method to find the element that occur only once 
    static int getSingle(int arr[], int n) 
    { 
        int ones = 0, twos = 0; 
        int common_bit_mask; 
          
        for(int i=0; i<n; 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*/
            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 method 
    public static void main(String args[]) 
    { 
        int arr[] = {3, 3, 2, 3}; 
        int n = arr.length; 
        System.out.println("The element with single occurrence is " + getSingle(arr, n)); 
    } 
} 
// Code contributed by Rishab Jain 