Recursion: Replace Loops using Recursion Explanation

JavaScript
#1

Tell us what’s happening:
Can someone help me to understand what is going on in the else return statement to pass these two tests:
sum([2, 3, 4], 1) should equal 2.
sum([2, 3, 4, 5], 3) should equal 9.
I’m having a very hard time wrapping my head around this problem.

Your code so far


function sum(arr, n) {
 // Only change code below this line
function sum(arr, n) {
 if (n <= 0) {
   return 0;
 } else {
   return sum(arr, n - 1) + arr[n-1];
 }
}
 // Only change code above this line
}

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.89 Safari/537.36.

Challenge: Replace Loops using Recursion

Link to the challenge:

#2

you have a function definifion inside a function definition, that’s not what you want

the outer function when called just return undefined, the inner one is never called

1 Like
#3

Oops just realized I entered an extra ‘}’ to the end of the code but this is the solution that was provided for this problem… Maybe there’s an error and that’s why I’m so confused,?

#4

you have twice the function definition, the outer one doesn’t have a return statement, so it returns undefined

2 Likes
#5

Must have been from copy/paste, can you help with what this return stack is returning?
return sum(arr, n - 1) + arr[n-1];

#6

hi there…guys where do you get this sum([2,3,4], 1)…the exemple doesnt exist on my page and I feel like I learn in blind mode…somehow I managed to guess the code and when I hit test, its starts to tell me :
sum([1], 0) should equal 0.
sum([2, 3, 4], 1) should equal 2…
from where???etc…I cant see anywhere on my page the example …!!!

#7

and this is happening with every lesson I passed until now…how can I understand something without having the example?..thx

1 Like
#8

The test cases are listed on the left side of your screen after the challenge description.

Here is a screenshot of where they are on mobile.

Screenshot_20201022-190829
Screenshot_20201022-1908291440×2960 289 KB

2 Likes
#9