Tell us what’s happening:
Hey guys,
I have passed this challenge somehow, but I didn’t understand the logic behind it.
Can anyone please explain it to me?
Your code so far
function sum(arr, n) {
// Only change code below this line
if ( n <= 0) {
return 0;
}
else{
return sum(arr, n - 1) + arr[n - 1] ;
}
// Only change code above this line
}
console.log(sum([1,2,3], 2));
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Challenge: Replace Loops using Recursion
Link to the challenge:
Okay, to break it down, if n is 0, what does the function return?
To put it another way and use the example at the end, what is the value of sum([1,2,3], 0)?
So if n is 0, the return value is 0.
So what if n is 1: sum([1,2,3], 1)?
n is not <= 0, so
return sum(arr, n - 1) + arr[n - 1]
So n - 1 is 0. sum([1,2,3], 0 is 0. So that says return 0 + 1, so 1.
So the return value of sum([1,2,3], 1) is 1.
So what if n is 2?
n is not <= 0, so
return sum(arr, n - 1) + arr[n - 1]
So n - 1 is 1. sum([1,2,3], 1) is 1. So that says return 1 + 2, so 3.
When trying to understand loops and/or recursion, it can be helpful to track the values at each step. Here’s an example:
