For a given array of integers, nums, return TRUE if it contains duplicates. Otherwise, return FALSE.

Constraints:

• $1 \leq$ nums.length $\leq 10^5$

• $-10^9 \leq$ nums[i] $\leq 10^9$

So far, you’ve probably brainstormed some approaches and have an idea of how to solve this problem. Let’s explore some of these approaches and figure out which one to follow based on considerations such as time and any implementation constraints.

The first solution that comes to mind while looking at this problem would be to iterate over all the elements of the nums array and compare each element with $(i-1)$ elements to check whether it is repeating. In this way, we will be able to find out if there are repeating duplicate numbers in the array. However, it is an expensive solution in terms of time complexity, since it comes out to be $O(n^2)$.

This can be improved in terms of time complexity. Let’s try to devise an optimized solution.

An efficient approach would be to keep track of numbers while iterating over nums. This way, we can find out if an element is repeating by just checking its occurrence instead of checking all the rest of the numbers in nums.

To achieve this, we will be using the hash map data structure records that is appropriate for problems like this. We iterate over the nums array, and for each number, we check if it exists in records or not. If it exists, then it means that the number is being repeated and the given array nums contains duplicates hence we return TRUE. If it is not the case, we add the current number to the records and move to the next number.

If all the numbers have been processed and we haven’t encountered any duplicates, we return FALSE, meaning that there is no duplicate in the given nums array.

Let’s look at the illustration below to better understand the solution.