Array Reduce Transformation (Transforms) - Leetcode 2626 - JavaScript 30-Day Challenge
Skills:
Algorithm Basics80%
Key Takeaways
Solves Leetcode 2626 Array Reduce Transformation using JavaScript
Full Transcript
hey everyone welcome back and let's write some more neat code today so today let's solve the problem array reduce transformation so we already talked about mapping and filtering but there's also another common function when it comes to functional programming and that is reducing conceptually it's similar to the other Transformations but in terms of using it it's a bit more complicated so that's what I'm going to be spending my time on in this problem first of all what even is reducing well it's all about aggregation let me actually show you what reducing is about let's say we're given this array and we want to find the sum of it well it's pretty easy to just pass this into like a library function and get the sum but I want to show you how we can do that with the reduce function that is built into arrays in JavaScript so we can say nums dot reduce this array but we have to actually tell it how we want to reduce the array how we want to aggregate this because aggregation can work in many ways we could be trying to find the total sum of this array or we could be trying trying to find the maximum value of this array the common theme here though is that we're given a list of values but we want to reduce them to a single value makes sense doesn't it now the function that we pass in to reduce has to kind of follow this header where it takes two parameters the first parameter is our initial value and the second parameter is going to represent a individual value from our list so what I mean here is when we take the sum of an array like this what do we want our initial value to be probably zero right so that's how we're going to call this function when we actually do pass it into reduce so let me actually do exactly that I'm going to pass in this function into reduce but we also have to pass in a second parameter to reduce to tell it what we want our initial starting value to be when we calculate the sum of this I'm going to initially set the starting value to zero now to actually fill in this function you might be getting the idea here this is going to be the initial value so what would we want to return if we're trying to take the total sum we probably can take the initial value and add it with n and then return that so what that would do for the first value is obviously 0 plus 1 and that's what it would return for just the first value here but then on the second iteration of the loop this is where something cool happens this function is going to be called again but it's not going to be past a zero for the initial value it's going to be passed in the previous value that we calculated which was one and if you take that one and add it with our current value n which is going to be 2 we get a 3 so then we would return 3 from here next we get to a seven so we take seven and add it with the previous value that we just calculated which was three so that's how this function is going to work but notice how most of that is abstract acted for us that's kind of the power behind functional programming we don't have to manage our own State we don't have to iterate through this list and just to prove to you that this works let me go ahead and console log it and as you can see the result is 19 as we would expect so now that we know a little bit about reduce let's actually solve the problem so the most trivial way to solve this problem is just to take the list of nums call reduce on them passing in whatever function we are given because that's how we want to reduce this with this initial value so basically that's what they were trying to teach us how reduce works even though they told us we're not allowed to use it but don't worry I'll solve it the imperative programming way in just a second let's run this to make sure that it works it does but there are other solutions to solve this problem so let's take a look let's recreate what this is actually doing explicitly we know initially our result is going to be whatever that initial value happens to be passed in and then we know we want to go through every single number in the input array nums take a second to think how you iterate through each number in an array well in Python we can use the keyword of that's usually the easiest way so for const n of nums in this case we don't need the index so we don't need the keyword in and with each value we just want to call that function and depending on which aggregation we're doing we could honestly pass in n and the initial value in either order but technically the correct order to pass it in is to pass in the initial value first and then pass in the current value that we're at in our list and then we would call this function and then update our result with that value but notice there is a small bug here when we call the function we don't want to pass in the initial value every single time I know that's a bit misleading because based on this over here on the left it kind of seems like we do but let's say the initial value is zero we don't want to keep adding zero with each element in the array we want to add the previous result which is over here thankfully stored in a variable and add that with n so I'm going to pass in the result into this function which initially is the initial value so it does work out for us after that's done I'm going to go ahead and return the result and run this to make sure that it works as you can see yes it does but there's one last Quick solution it's kind of a halfway solution between this reducing functional programming solution and this like fully imperative solution I guess not entirely imperative because we could have actually iterated through this with an index that we like explicitly increment but I'm sure you already know how to do that so I won't bother with it too much the other way to solve this problem would be to take uh let me erase this that list of nums and there's another function that belongs to every list it's called for each and basically it'll call some function that we pass into it on each element in the array so how can this be used to solve this problem well first let's pass in a function I'm going to pass in an anonymous function which we can do just like this we have our parameters here which parameter are we passing in well we're going to go through each number so I'm going to have n for each number in the input and this is our block what do we want to return well in this case we don't really need to return anything we just need to update our outside State we need to update our result value by setting it equal to the function being called with the result and the individual value that we're currently at after running this our result variable will be updated so we can go ahead and run this to make sure that it works and as you can see yes it does but I guess it's a little bit slower those are all the solutions I wanted to discuss you might be starting to see the power of functional programming or maybe you're starting to hate it I don't know but thanks for watching if you found this helpful please like And subscribe and hopefully I'll see you pretty soon
Original Description
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Solving day 6 of leetcode's 30-day javascript challenge. Today we continue with functional programming concepts using the Reduce operation.
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⭐ BLIND-75 PLAYLIST: https://www.youtube.com/watch?v=KLlXCFG5TnA&list=PLot-Xpze53ldVwtstag2TL4HQhAnC8ATf
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Problem Link: https://leetcode.com/problems/array-reduce-transformation/
0:00 - Read the problem
0:30 - Built-in Reduce usage
3:15 - Reduce solution
3:45 - For-loop solution
5:22 - For-each solution
leetcode 2626
#neetcode #leetcode #python
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Chapters (5)
Read the problem
0:30
Built-in Reduce usage
3:15
Reduce solution
3:45
For-loop solution
5:22
For-each solution
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Tutor Explanation
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