arrays - Find ith permutation in javascript -

given array arr of size n, , and index 0<i<n! want return ith permutation.

i able write method gets permutations:

function permute (arr) {   var permutations = [];   if (arr.length === 1) {     return [ arr ];   }    (var = 0; <  arr.length; i++) {      var subperms = permute(arr.slice(0, i).concat(arr.slice(i + 1)));     (var j = 0; j < subperms.length; j++) {       subperms[j].unshift(arr[i]);       permutations.push(subperms[j]);     }   }   return permutations; } 

how trim 1 branch of recursion ?

you use factorial of length of array helper getting wanted permutation.

basically algorithm calculates indices of array , reassembles result upon.

function getn(n, array) {      var f,          l = array.length,          indices = [];        array = array.slice();      while (l--) {          f = factorial(l);          indices.push(math.floor(n / f));          n %= f;      }      return indices.map(function (i) {          return array.splice(i, 1)[0];      });  }    function factorial(num) {      var result = 1;      while (num) {          result *= num;          num--;      }      return result;  }    var i, l,      array = [1, 2, 3, 4];    (i = 0, l = factorial(array.length); < l; i++) {      console.log(i, getn(i, array).join(' '));  }

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