JavaScript Algorithms - 7 - Fibonacci Sequence 

Hey pal, please is it possible for you to send how you traced it out steps on paper? I’m finding it difficult to do the same 😭😭😢

@@ogucharles2800 u stilll need help brother?

@@bzchii7474 I do :((((

@@sam.antonielli ask away

@@bzchii7474 I'm a rising junior right now in college, transferring from mechanical engineering into cs, im learning JavaScript right now on my own that way I have a decent understanding of algs and data structures and just programming in general before the fall, but it is sooooo confusing and I feel absolutely lost, is that normal? should I just keep pushing and any advice on learning?

This is what I was thinking as well

I believe he wants it so that if I enter "2", it indicates two numbers in the array; if I enter "7", it signifies seven Fibonacci numbers in the array. However, if I enter "7", it doesn't refer to the 7th Fibonacci number; instead, it indicates that there should be seven Fibonacci numbers in the array.

You're missing the 0th index. 0-6 is a length of 7. The syntax in the video is correct.

I have also implemented it this way! :))

did the exact same thing😂.

thank you for this. This makes a tad bit more sense, and easier to follow.

To fix this, line 6 could be: return fib.slice(0, n);

@@mstalcup It will work but it is not a good solution as slice will have its own time complexity of O(n) which would not be good for large input size. However, adding ' If condition ' would be a good choice in my opinion.

here it works fine and it's not affecting time complexity function fibonacci(n){ const fib = [0, 1]; if(n == 0){ return null; } else if(n == 1){ return 0; } else { for(let i = 2; i < n; i++){ fib[i] = fib[i - 1] + fib[i - 2]; } return fib; } }

It actually doesn't make more sense. It's slower. It works and is a good example of recursion but it makes the opposite of more sense. Your recursive method is O(2^n) while the for loop is O(n). Just because the code uses fewer characters doesn't make it 'make more sense'. IMO, faster is always better when writing functions and methods not matter how many lines the code is.

How can we get the sequence with recursion, not just the nth value???

​@@DriveandThriveHow is it recursion it executes once? It is a constant O(1)

I don't know if you still need the answer but I'll give one so it can help others. In Javascript, Arrays are also Objects with properties inside, and "length" is one of them, Arrays keep track of the length so accessing the length is an O(1) operation not an O(n) (i.e. it's not actually counting all items to get the length every time you do "arr.length"). So to answer your question, using a "while" loop is an O(n) operation and everything inside are O(1) operations, so the result is still O(n) or linear.

Actually fib is declared as an array which in turns is an object. You can change the value inside array nothing wrong with that. But you cant do that for primitives values like number, string, boolean.

@@khairiyusoff5040 Okay, Thanks 🙂

Yes we wont be changing the array to say a string or number...so const makes sense fib wont be changing. Only the values in the array will change which is a different matter. If you try to assign fib = 3; or something const will kick in to protect it. If const somehow prevented arrays from changing it wouldn't be good.

@@DriveandThrive 🙌🙂

You are correct, however the big picture is that the -2 means very little with a larger input, and therefore it is normal to discard any constant values. If you look at the code there are several operations that are run n (-2) times you have the comparison of i < n you have the increment of i, you have the assignment of the array at index i you also have the addition. So you could also say O(4(n-2)). Again this multiple is dropped as the point of the notation is to compare constant / linear / quadratic / exponential functions in general terms.

This doesn't return array

Very true.

i is an index of the elements in the array. The element's index in an array counts from 0 , so 0,1,2,3,4...etc. We already have const fib= [0, 1] (this is equal to i=1), so we are starting with i=2 and looking for elements until the index is equal to n. Hope that helps!

const only works for primitive data types and not for non primitive data types like arrays

it is immutable only if the entire array is declared again. it is allowed to add or remove values. the same happens with objects

You can do this to an array: const arr = [1,2]; arr.push(3); But not this: const arr=[1,2]; arr=[1,2,3];

const implies memory creation for the respective object is constant . so arrays and objects are mutable or we can change the internal values but the reference to the memory is same.

It is the same,remember that accesing arr[index] is O(1) constant same as arr.push.Both ways have same time complexity.Choose what you want

@@oscargm1979 right on, thanks!

@@allisonposey1946 thank you alisson

@@allisonposey1946 The fibonacci number is the sum of last two numbers in array. Hope it help