Build a Permutation Generator - Build a Permutation Generator

JavaScript
1

Tell us what’s happening:

my test is logging the correct result, but I feel like for some reason when I call the method it does’nt return the correct array, what am I missing here?

Your code so far

function permuteString(string, prefix = '', array = []){
  if(string.length === 0) {
    array.push(prefix);
    
    if(array.length == getPermuteAmount(prefix.length))
    {
      console.log([...new Set(array)]);
      return [...new Set(array)];
    }
  }
  
  for(const char in string){
    let s = string.split("");
    s.splice(char, 1);
    s = s.join("");
    permuteString(s, prefix + string[char], array);
  }
}

function getPermuteAmount(length){
  let amm = 0;
  let len = length;
  while(len > 0){
    amm += len;
    len--;
  }
  return amm;
}

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/134.0.0.0 Safari/537.36 Edg/134.0.0.0

Challenge Information:

Build a Permutation Generator - Build a Permutation Generator
https://www.freecodecamp.org/learn/full-stack-developer/lab-permutation-generator/build-a-permutation-generator

2

I don’t think you can return in the middle of the recursion like this, you need to move the return to the end of your function…

I don’t really understand it right now but I think the console.log works because it logs it after unwinding the call stack…

but you can’t return where the console.log is or it returns too early, without finishing all of the recursive calls that have stacked up.

This isn’t a good explanation, but do you see what I’m thinking?

3

not sure if that is what you ment but just tried movind the returning condition to after the recursive call like this:

function permuteString(string, prefix = '', array = []){
  
  for(const char in string){
    let s = string.split("");
    s.splice(char, 1);
    s = s.join("");
    permuteString(s, prefix + string[char], array);
  }
  
  if(string.length === 0) {
    array.push(prefix);
    
    if(array.length == getPermuteAmount(prefix.length))
    {
      console.log([...new Set(array)]);
      return [...new Set(array)];
    }
  }
}

and it still didn’t work, is this what you ment?

4

I tried moving it to the very end of the function, the last point before the last bracket.

I hope someone could have a better explanation though.

5

don’t really understood how it works but got it to work, will try to figure out why :sweat_smile: thanks for the help.

6

Me neither… I was following some kind of intuition.

@lasjorg @JeremyLT @ILM Found the solution to this but I’m not really able to explain why it works. Any insight here?

8

I think we may have to open an issue to discuss this exercise. I gave it to Science on discord and she’s struggling with it too. I think the requirement to use a single recursive function (with no helper) makes it extra complex.

9

Agree! My solution has more console.log() statements and comments in it than code to try to understand how it works. Very tough challenge.

10

This is a tough challenge indeed but I wrestled with it for some time and eventually figured it out.
Precisely because I found it so tough (and recursion can be a headache), I also wrote a very detailed breakdown of exactly how it works.
If anyone’s interested in seeing it, please let me know!

11

There’s a github issue for it now.
So pls put your break down there in case it helps them clarify it.

12

I am interested in your breakdown because my code doesn’t go all the way, the recursion ends too soon and I think it’s because I don’t really know how to go about the challenge. But anyway, I am interested in your breakdown…

14

If you have a question about a specific challenge as it relates to your written code for that challenge and need some help, click the Get Help > Ask for Help button located on the challenge.

image
image493×196 5.09 KB

The Ask for Help button will create a new topic with all code you have written and include a link to the challenge also. You will still be able to ask any questions in the post before submitting it to the forum.

Thank you.