No Repeats Please, Wrong Perm Amount

No Repeats Please, Wrong Perm Amount
0

#1

Tell us what’s happening:
Greetings! I tried using Heap’s algorithm for this puzzle, however the number of permutations created by the algorithm vs the mathematical calculation are different, for example:
“aabb” is calculated at 4! = 24 permutations, however my Heap’s algorithm only logs 21. Any idea why it doesn’t account for every permutation?

Your code so far


function permAlone(str){
  
  var perms = [];
  let arr = str.split('');

//add a prototype to swap letters in array
  Array.prototype.swap = function (x,y) {
    var b = this[x];
    this[x] = this[y];
    this[y] = b;
    return this;
  }

 //Deploys Heap's algorithm
  function generate(n,arr){
    if (n === 1){
      perms.push(arr.join('')); 
    }
    else { 
      for (var i = 0; i < n-1; i++){
        generate(n-1, arr);
        if (n % 2 == 0){
         perms.push(arr.swap(i, n-1).join(''));
        }
        else { 
          perms.push(arr.swap(0,n-1).join(''));

        }
      }
    }
  }
 generate(str.length,arr);

//check Heap 
//console.log(perms.length);
//check Factorial
//console.log(getPerms(str,false));


 let result = perms.filter(word => {
  return /([a-z])(\1)/g.test(word) == false;
 });

 return result.length;

  
 //-----------This function is not actually used, I used it as a benchmark for the correct num of permutations---------------------------------------
 //loops through the length of str, and pushes index value into array
 function getPerms(str,num){
  if (str){
  let arr = [];
   for (var i = str.length; i > 0; i--){
     arr.push(i);
   }
   //calc perms by reducing to get factorial 
  return arr.reduce((a,b) => a*b);
  }
  //does the same, just replaces str w/ number
  else if (num){
     let arr = [];
   for (var i = num; i > 0; i--){
     arr.push(i);
   }
  return arr.reduce((a,b) => a*b);
  }
 }
 //---------------------------------------------

}
permAlone("abcdefa");

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36.

Link to the challenge:
https://learn.freecodecamp.org/coding-interview-prep/algorithms/no-repeats-please/