Algorithm Scripting: Mutations

JavaScript
1

Tell us what’s happening:
So I feel stuck. I’ll put comments down below with my code to clarify what I’m attempting.

It seems as though my code is broken here:

  if (firstArr.indexOf(secondArr[i]) > 0)

because the console logs true and then false. It’s as if it is skipping over the first character/first string in the array.

I can’t figure out why.

Your code so far


function mutation(arr) {
let comparison = 0; //I'm incrementing this variable by 1 for each character from the second string that is contained in the first string. I then compare the number with the length of the second string. 
let firstStr = arr[0].toLowerCase();
let secondStr = arr[1].toLowerCase();
let firstArr = firstStr.split("");
let secondArr = secondStr.split("");
for (let i = 0; i <= secondArr.length; i++) {
  if (firstArr.indexOf(secondArr[i]) > 0) {
    comparison++;
    console.log(comparison)
    return (comparison === secondArr.length);
  } 
}

return false;
}

mutation(["hello", "hey"]);

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Challenge: Mutations

Link to the challenge:

2

what does indexOf return if the item is in the first position of the array?

3

It returns 0 and zero cannot be greater than 0. I change it to -1 and it doesn’t work, and I changed it to >= 0 and still nothing.

Am I making this more complicated than it needs to be?

4

I made some changes, but I still cannot quite understand why my code isn’t working.

Maybe I’ve not logged the right thing yet to land on the problem.

I’m now logging these and getting their respective results:

console.log(firstArr) // [ 'h', 'e', 'l', 'l', 'o' ]
  console.log(secondArr[i]) // h
  console.log(firstArr.indexOf['h'])  // undefined
  console.log(secondArr.length)  // 3
  console.log(current)  // 0 
  console.log(current > -1)  // true

I’m not sure why that one is coming back as undefined

function mutation(arr) {
let comparison = 0; 
let firstStr = arr[0].toLowerCase();
let secondStr = arr[1].toLowerCase();
let firstArr = firstStr.split("");
let secondArr = secondStr.split("");
for (let i = 0; i < secondArr.length; i++) {
  let current = firstArr.indexOf(secondArr[i]);
  console.log(secondArr.length) //logs 3 as expected
  console.log(current) // logs 0 as expected
  console.log(current > -1) // logs true as expected
  if ( current > -1) {
    comparison++;
    return (comparison == secondArr.length);
  } 
}

return false;
}

mutation(["hello", "hey"]);
5

is that the correct syntax for indexOf?

when do you have to return true and when do you have to return false?

1 Like
6

Okay I see my problem with the syntax. It should have had parentheses.

I also see that the return should occur after the for loop has run it’s course. Correct me if I’m wrong, but the problem was that I was returning the comparison before the loop had completed?

7

you need to return true if there are all letters, but you can return false even if just one letter is not found

your issue is that you were just returning false

consider this:

first letter is present, current is higher than -1
but return comparison == secondArr.length returns false becuase comparison is just at 1

no letter is present:
current is never higher than -1
the loop is exited and return false is executed

1 Like
8

Thank you for your help! I greatly appreciate it!

9