Difficulty: Easy
Topics: Hash table, bit manipulation.
This solution uses the bitwise XOR operator to return the unique value in the array.
To illustrate the bitwise XOR operation using the given Example 2 from LeetCode page:
Input: [4,1,2,1,2]
Bitwise XOR operation with 0 on the elements:
0 ^ 4 ^ 1 ^ 2 ^ 1 ^ 2
> 4
We want to go through every element in the array, perform the bitwise XOR operation, and return a single value output. Instead of the conventional for loop, we use array's reduce() function to achieve this, which is more succinct.
Time complexity: O(n) because we go through every elements in the array once.
Space complexity: O(1) because the memory used is always the same regardless of the number of elements.