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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.
Example:
int [] a = { 1,5,6,2,1,6,4,3,2,5,3}; output: 4
Approach:
Brute Force:
Use nested loops and compare each element in the array with all other elements and track the element which is nonrepeated.
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)
Use XOR
 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.
Output:
Element appear only once in array – 4