Determine if an array has repeated element by sorting the array

Question

 <script>
  var arr = [];

  function repeater(str){
    for (var i=0; i<str.length;i++)
      {arr.push(str[i])}
      arr.sort()
    for (var g=0;g<arr.length;g++) {
    if (arr[g]==arr[g+1])
     {return false}

      else {return true}

    }
  }

document.write(repeater("jrtgrt"))
    console.log(arr)
</script>

Create a function that takes a string and returns either true or false depending on whether or not it has repeating characters.

The array is working by console, but the second part doesn't seem to be running.

Wai Ha Lee · Accepted Answer · 2019-12-05 17:04:49Z

1

Your loop is terminating after the first comparison because either way return is called.

<script>
    var arr = [];

    function repeater(str) {
        for (var i = 0; i < str.length; i++) {
            arr.push(str[i])
        }
        arr.sort()
        for (var g = 0; g < arr.length - 1; g++) {
            console.log(arr[g], arr[g + 1])
            if (arr[g] == arr[g + 1]) {
                return true
            }
        }
        return false;
    }

    document.write(repeater("12s35sd46"))
    console.log(arr)
</script>

edited Dec 5, 2019 at 17:04

Wai Ha Lee

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answered Dec 5, 2019 at 16:29

paul

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Comments

J F Fitch · Accepted Answer · 2019-12-05 17:00:07Z

0

There are a few ways to simplify your code.

You don't need a for loop to create an array from a string. You can use the split function.

arr = str.split("");

Your entire function can literally be simplified to this using a regular expression.

function repeater(str) {
    return /(.).*\1/.test(str);
}

Here's an explanation of each part of the regular expression:

(.) any character, capture to use later
.* any character any number of times
\1 first captured character

answered Dec 5, 2019 at 17:00

J F Fitch

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2 Comments

Jiang Yuxin Over a year ago

Hi thank you for this. But I just started learning js and I would rather to stay at simple and basic methods for now.

Klaycon Over a year ago

@JiangYuxin Perfectly reasonable but the suggestion to use str.split("") is a good one and would improve your code. It's a good idea to learn the array and string helpers early - they are simple and helpful.

Peter Seliger · Accepted Answer · 2019-12-05 18:25:03Z

An approach might not necessarily rely on an array's sort method. One, for instance, could stepwise shorten the list of characters and then, via an array's some method, determine whether the current character has a duplicate counterpart in the yet remaining list of characters. Thus one also keeps the amount of iteration cycles low ... example ...

function hasDuplicateChars(stringValue) {
    var hasDuplicate = false;

    var charList = stringValue.split('');
    var char;

    // continue taking the first entry of `charList` while mutating the latter.

    while (!hasDuplicate && (char = charList.shift())) { // `char` either will be a string or a undefined value.

      hasDuplicate = charList.some(function (listItem) { return (char === listItem); })
    }
    return hasDuplicate;
}

console.log('hasDuplicateChars("") ? ', hasDuplicateChars(""));
console.log('hasDuplicateChars("x") ? ', hasDuplicateChars("x"));
console.log('hasDuplicateChars("abcdefghijklmnopqrstuvwxyz") ? ', hasDuplicateChars("abcdefghijklmnopqrstuvwxyz"));

console.log('hasDuplicateChars("TheQuickBrownFox") ? ', hasDuplicateChars("TheQuickBrownFox"));
console.log('hasDuplicateChars("Hallo, world.") ? ', hasDuplicateChars("Hallo, world."));
console.log('hasDuplicateChars("  ") ? ', hasDuplicateChars("  "));

.as-console-wrapper { max-height: 100%!important; top: 0; }

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