Fibonacci Sequence Recursion Explained (JavaScript)

We walkthrough an example problem: "Find the nth number in the Fibonacci Sequence" to better understand how to code recursive solutions to problems.

5:45 - Recursive explanation begins (video starts with a non-recursive iterative solution)

First, we solve the problem with a non-recursive JavaScript solution which uses shifting "pointer" variables to calculate the numbers of the sequence.

Next, we look at a recursive solution and see how functions are pushed to the call stack to solve specific branches of a recursive tree. We begin to understand the amount of calculation behind a recursive solution and start to see areas for improvement. That is we begin to see places where we could improve performance by memoization, or remembering the values of past calculations.

[amitbhosale]

thankyou for explaining this code in such a simple and beautiful way I really loved it your channel is worth subscribing

[bubbyprime]

Now I see why memoization is helpful. @11:06 where you said were not remembering the value of fib(3). I didn't realize that this function had to call fib(3) again. Thank you for walking through this. I know this is about explaining mainly recursion, but I've been going through different videos trying to understand how the memoization works and you just made it click.

[matthewc.]

10/10 explanation. Been struggling to put these pieces together myself for hours and your video made it crystal clear. Thanks so much!!!

[internetdrew]

This was THE video that helped me understand this and taught me high to climb through it. The only thing I see here that is an issue is that the fib sequence actually starts at 0, so you'll want your "prev" variable to be 0, not 1, to be truly accurate. But if you just want to understand the logic in as plain English as possible, this is IT!

[dolicious]

this was such a good explanation !! when I was calculating my fib function using math I was not understanding how the correct number in the sequence was getting outputted but I forgot about calculating the base case ! it was very helpful going through line by line and each call stack. I admit I had to watch 5 times before I really got it but a great video and great explanation!

[shahriarahmedraktim]

this video has finished my all thank you dear

[criaturaimaginaria]

hey you... you´re my hero, this is the best explanation of the fibonacci sequence I´ve ever seen. Very beautifully detailed and clear. thanks!

[joyannejoy]

Amazing walkthrough of what's going on in the call stack! That really clarified things for me!

[nauilnil]

Thank you so much for such a detailed explanation!

[KwabenaAgyemanLipsy]

Really insightful explanation. concise and straight to the point. Thank you!!!

[albatalu-ali]

This is the best explanation i've ever seen. Protect this man at all cost!

[bobthehuntsman]

Thank you for the great explanation! Very clear and easy to comprehend.

[robbiemclaughlin]

Video was awesome, was having a hard time understanding the process between the input and output of a recursive function, this cleared it up, thank you for the help! Also what color theme are you using here?

[mahfujhossain]

A very elaborated explanation.Thank you!

[TheToxicPepsi]

This is a great video, thank you for making it !

[froylanrodriguez]

Hey I am a bit confused, you said we do not remember the value of fib(3) when trying to calculate fib(5) since it was popped off the stack, which made 100% sense @11:06; however, earlier when calculating fib(4) you said "we just returned the value of fib(3) so we know it" but how is this possible if it was popped off the stack?? @9:20 is it because it was the previous calculation of fib(4)? sorry for the weird question, loved the video tho man, great stuff!

[AddictedToCode]

function fib(n) {
let fibList = [];
if (n < 2) {
fibList.push(0);
} else {
let prev = 0;
let curr = 1;
fibList.push(prev, curr);
for (let i = 2; i < n; i++) {
const next = prev + curr;
prev = curr;
curr = next;
fibList.push(curr);
}
}
console.log(fibList);
}

[kirs]

Fantastic video! Thank you! Clearly demonstrates a confusing topic. Do you have a video showing how you got the dubugger to run correctly in VSC?

[tidumarco]

Thanks a lot for your great explanation! How did you configured your launch.json to automatically show the call stack and variables values? I can't find a way to do it. Thanks!

[byevrolex]

why is i set to 2 and not 0 in the while loop?