Function swap

src/next-permutation.js:3–7

(a, i, j)

// https://leetcode.com/problems/next-permutation/description/

const swap = (a, i, j) => {
  const t = a[i];
  a[i] = a[j];
  a[j] = t;
};

const sort = (a, i) => {
  for (; i < a.length; i += 1) {