This post is completed by 2 users

  • 1
Add to List

228. Find the only element in array which appears only once

Objec­tive: Given an array of integers, all the elements appear twice but one element appears only once. Write an algorithm to find that element.


int [] a = { 1,5,6,2,1,6,4,3,2,5,3};
output: 4


Brute Force:

Use nested loops and compare each element in the array with all other elements and track the element which is non-repeated.

Time Complexity: O(n^2)

Use Hashing:

  • Store the count of each element in a hash map.
  • Iterate through the hash map and return the element which has count 1.

Time Complexity: O(n) , Space Complexity: O(n)


  • We know that A XOR A = 0.
  • If we XOR all the elements in the array, all the elements which are repeated twice will become 0, and remaining will the element which is appearing only once.


Element appear only once in array – 4