**Objective**: Given an array of integers, all the elements are appear twice but one element which 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 array with all other elements and track the element which is non-repeated.

Time Complexity: O(n^2)

**Code**:

**Use Hashing:**

· Store the count of each element in a hash map.

· Iterate through hash map and return the element which has count 1.

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

**Code**:

**Use XOR**

· We know that A XOR A = 0.

· If we XOR all the elements in array, all the elements which are repeated twice will become 0 and remaining will the element which is appearing only once.

**Code**:

**Output**:

Element appear only once in array – 4