how to find duplicate in string and return index js

Question

need to return index of second occurrence if no duplicate return not found

const forAll = (str) => {
  var forAllmini;
  for (var i = 0; i < str.length; i++) {
    forAllmini = (str[i] != str[i+1]) ? 'not found': `@ index ${i}`;
  }
  return forAllmini
}

console.log(forAll('carrot'))

i tried this but i only get 'not found'

You overwrite `forAllmini` every time you loop, so it's only returning the last comparison. Once you find it, break your loop and return. — mykaf, Aug 18 '22 at 13:49
Check this answer https://stackoverflow.com/questions/33656708/check-for-repeated-characters-in-a-string-javascript — Carlos Osvaldo Chao Cortes, Aug 18 '22 at 13:52

score 3 · Accepted Answer · answered Aug 18 '22 at 13:54

3

If you need to find repeated chars you can use a set and check it like this:

const forAll = (str) => {
  const visited = new Set();
  for (var i = 0; i < str.length; i++) {
    if(visited.has(str[i])) return `@ index ${i}`;
    visited.add(str[i]);
  }
  return 'not found'
}

console.log(forAll('carrot'))

answered Aug 18 '22 at 13:54

mgm793

1,968
15
23

thanks but why are you using set and not something else – Aug 18 '22 at 13:59
1

because set allows you to check if the value exist in the "array" in a better efficient way than others – mgm793 Aug 18 '22 at 14:01
i don't understand why u add str[i] and why it doesn't work without adding – Aug 18 '22 at 14:10
I add str[i] because once you visit this letter it's visited – mgm793 Aug 19 '22 at 06:33

score 1 · Answer 2 · answered Aug 18 '22 at 13:51

1

Because the forAllmini is overwritten:

const forAll = (str) => {
  for (var i = 0; i < str.length; i++) {
    if(str[i] == str[i+1]) return `@ index ${i}`;
  }
  return 'not found';
}

console.log(forAll('carrot'))

answered Aug 18 '22 at 13:51

Chang Alex

505
3
11

score 1 · Answer 3 · answered Aug 18 '22 at 13:53

You need to break your for like this:

const forAll = (str) => {
  var forAllmini;
  for (var i = 0; i < str.length; i++) {
    forAllmini = (str[i] != str[i+1]) ? 'not found': `@ index ${i}`;
    if (forAllmini != 'not found') {
      break;
    }
  }
  return forAllmini
}

console.log(forAll('carrot'))

score 0 · Answer 4 · answered Aug 18 '22 at 13:59

0

You were mutating the variable in every iteration, and not breaking out when duplicate was found.

const forAll = (str) => {
  for (var i = 0; i < str.length; i++) {
    if((str[i] == str[i+1])) return `@ index ${i}`
  }
  return "not found"
}

console.log(forAll('carrot'))

answered Aug 18 '22 at 13:59

Never Serious

91
4

so how can breake it? – Aug 19 '22 at 18:26
i thought and i got it, thanks – Aug 19 '22 at 18:47

score 0 · Answer 5 · answered Aug 18 '22 at 14:00

Loop through the string one char at a time, starting from index 1. You don't need to save intermediate results, just return from a loop to break out of it.

The problem with your forAllmini variable is that it is overridden on each loop iteration.

function forAll(input) {
  for (let i = 1; i < input.length; i += 1) { // start at index 1, not 0!
    if (input[i - 1] === input[i]) { // check if previous char === current char
      return `@ index ${i - 1}`; // return index of first doubled character
    }
  }
  return 'not found';
}



console.log(forAll('carrot'));
console.log(forAll('none'));

how to find duplicate in string and return index js

5 Answers5