Math Challenge print the next largest number after shuffling using javascript

Question

Have the function nextLargest(num) take the num parameter being passed and return the next number greater than num using the same digits. For example: if num is 123 return 132, if it's 12453 return 12534. If a number has no greater permutations, return -1 (ie. 999).

Examples

Input: 11121
Output: 11211
Input: 41352
Output: 41523

var permute = (function () {
    return permute;

    function permute(list) {
        return list.length ?
            list.reduce(permutate, []) :
            [[]];
    }
    
    function permutate(permutations, item, index, list) {
        return permutations.concat(permute(
            list.slice(0, index).concat(
            list.slice(index + 1)))
            .map(concat ,[item]));
    }
    
    function concat(list) {
        return this.concat(list);
    }

}());

console.log(JSON.stringify(permute([1,2,3,4])));

my output : [[1,2,3,4],[1,2,4,3],[1,3,2,4],[1,3,4,2],[1,4,2,3],[1,4,3,2],[2,1,3,4],[2,1,4,3],[2,3,1,4],[2,3,4,1],[2,4,1,3],[2,4,3,1],[3,1,2,4],[3,1,4,2],[3,2,1,4],[3,2,4,1],[3,4,1,2],[3,4,2,1],[4,1,2,3],[4,1,3,2],[4,2,1,3],[4,2,3,1],[4,3,1,2],[4,3,2,1]]

expected output :

Input: 11121
Output: 11211
Input: 41352
Output: 41523

Answer 1

Assuming the permute function as given that you shared in your question, the following straightforward approach should solve the question.

It is not very efficient, however. Probably, a better strategy could be found working with a cleverly chosen sequence of transpositions only.

function nextLargest(input) {
  let x = input.toString();
  let p = permute([...x]);
  let result = Infinity;
  for (let n of p) {
    let y = n.join('')*1;
    if (y > input && y < result) result = y; 
  }
  return result < Infinity ? result : -1;
}
  
console.log(nextLargest(1234));  // <<< gives 1243