Two Ways of Solving The Contains Duplicate Question


It took me quite some time to solve this problem because I didn’t know how to approach it. The key in solving algorithm problems is to understand the question and look out for any clues that can be given. Note that this problem will be solved in JavaScript!

The question is asking us to return a boolean value if an array of integers contains any duplicate values. There are various ways we can solve this question, but when trying to solve any problem that has to do with uniqueness we should think about Sets. Sets are objects that contain a collection of values and those values have to be unique. For more information on Sets() check out the resources section located on the bottom of this blog.

First Solution:

This is how our code should look like as of right now:

The next step is to iterate through each element inside of the nums array and see if the current number inside the array exists in the set newSet. We can use the for statement syntax, but I’ll be using the for of statement syntax just to show the different ways of solving this question. Check out the resources section below for more info on for and for of loops. If the current number on the array doesn’t exist in the set, then that number should be added in newSet. If the current number does exist, then we return true since that number already exists inside of newSet. Outside of the for of loop or once the loop is finished, I would recommend setting the default boolean value to false. We would do this because if all of the logic inside the for of loop isn’t met, that means that the array doesn’t contain any duplicates.

According to LeetCode, this solution is actually one of the best approaches, here are the results when submitting the solution on Leetcode:

Second Solution:

Overall it’s pretty good, but we can always figure out ways in which we can improve our code. For instance, we can still create a Set for this problem, but we don’t really need to iterate over anything. For this next solution, we can just compare the size of the set (newSet) and the length of the array (nums). If they’re equal to each other then that means that there are no duplicates in the array and if the array length is bigger then there’s a duplicate. Remember that sets are objects that hold unique values! Here’s the solution:

Here we can see that on line 3 I created the set, but also passed in numsas an argument. I’m doing this because the set (newSet) needs to have values inside, otherwise we will be working with an empty set. Here’s what newSet with the nums array as an argument and the nums array alone look like when you use console.log():

As we can see, the array has 4 elements while the set has 3 values. Again this is because sets hold unique values, so in this case the set is not going to have the number 1 again.

Here are the results when submitting this solution on LeetCode:


I hope this blog was able to help out in any way! I’m open to hearing about more solutions that may work so please reach out! Check out the resources section below for more information on sets!