freeCodeCamp/curriculum/challenges/spanish/08-coding-interview-prep/algorithms/no-repeats-please.spanish.md

---
id: a7bf700cd123b9a54eef01d5
title: No Repeats Please
localeTitle: No se repite por favor
challengeType: 5
---

## Description
<section id='description'> 
Devuelve el número de permutaciones totales de la cadena proporcionada que no tienen letras consecutivas repetidas. Supongamos que todos los caracteres de la cadena proporcionada son únicos. 
Por ejemplo, <code>aab</code> debería devolver 2 porque tiene 6 permutaciones totales ( <code>aab</code> , <code>aab</code> , <code>aba</code> , <code>aba</code> , <code>baa</code> , <code>baa</code> ), pero solo 2 de ellas ( <code>aba</code> y <code>aba</code> ) no tienen la misma letra (en este caso, <code>a</code> ) repitiendo. 
Recuerda usar <a href='http://forum.freecodecamp.org/t/how-to-get-help-when-you-are-stuck/19514' target='_blank'>Read-Search-Ask</a> si te atascas. Trate de emparejar el programa. Escribe tu propio código. 
</section>

## Instructions
<section id='instructions'> 

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>permAlone(&quot;aab&quot;)</code> debe devolver un número.
    testString: 'assert.isNumber(permAlone("aab"), "<code>permAlone("aab")</code> should return a number.");'
  - text: <code>permAlone(&quot;aab&quot;)</code> debe devolver 2.
    testString: 'assert.strictEqual(permAlone("aab"), 2, "<code>permAlone("aab")</code> should return 2.");'
  - text: <code>permAlone(&quot;aaa&quot;)</code> debe devolver 0.
    testString: 'assert.strictEqual(permAlone("aaa"), 0, "<code>permAlone("aaa")</code> should return 0.");'
  - text: <code>permAlone(&quot;aabb&quot;)</code> debe devolver 8.
    testString: 'assert.strictEqual(permAlone("aabb"), 8, "<code>permAlone("aabb")</code> should return 8.");'
  - text: <code>permAlone(&quot;abcdefa&quot;)</code> debe devolver 3600.
    testString: 'assert.strictEqual(permAlone("abcdefa"), 3600, "<code>permAlone("abcdefa")</code> should return 3600.");'
  - text: <code>permAlone(&quot;abfdefa&quot;)</code> debe devolver 2640.
    testString: 'assert.strictEqual(permAlone("abfdefa"), 2640, "<code>permAlone("abfdefa")</code> should return 2640.");'
  - text: <code>permAlone(&quot;zzzzzzzz&quot;)</code> debe devolver 0.
    testString: 'assert.strictEqual(permAlone("zzzzzzzz"), 0, "<code>permAlone("zzzzzzzz")</code> should return 0.");'
  - text: <code>permAlone(&quot;a&quot;)</code> debe devolver 1.
    testString: 'assert.strictEqual(permAlone("a"), 1, "<code>permAlone("a")</code> should return 1.");'
  - text: <code>permAlone(&quot;aaab&quot;)</code> debe devolver 0.
    testString: 'assert.strictEqual(permAlone("aaab"), 0, "<code>permAlone("aaab")</code> should return 0.");'
  - text: <code>permAlone(&quot;aaabb&quot;)</code> debe devolver 12.
    testString: 'assert.strictEqual(permAlone("aaabb"), 12, "<code>permAlone("aaabb")</code> should return 12.");'

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js
function permAlone(str) {
  return str;
}

permAlone('aab');
```

</div>



</section>

## Solution
<section id='solution'>


```js
function permAlone(str) {
  return permutor(str).filter(function(perm) {
    return !perm.match(/(.)\1/g);
  }).length;
}

function permutor(str) {
  // http://staff.roguecc.edu/JMiller/JavaScript/permute.html
  //permArr: Global array which holds the list of permutations
  //usedChars: Global utility array which holds a list of "currently-in-use" characters
  var permArr = [], usedChars = [];
  function permute(input) {
    //convert input into a char array (one element for each character)
    var i, ch, chars = input.split("");
    for (i = 0; i < chars.length; i++) {
      //get and remove character at index "i" from char array
      ch = chars.splice(i, 1);
      //add removed character to the end of used characters
      usedChars.push(ch);
      //when there are no more characters left in char array to add, add used chars to list of permutations
      if (chars.length === 0) permArr[permArr.length] = usedChars.join("");
      //send characters (minus the removed one from above) from char array to be permuted
      permute(chars.join(""));
      //add removed character back into char array in original position
      chars.splice(i, 0, ch);
      //remove the last character used off the end of used characters array
      usedChars.pop();
    }
  }
  permute(str);
  return permArr;
}

permAlone('aab');

```

</section>