reverseNodesInKGroups.js

// Definition for singly-linked list:
// function ListNode(x) {
//   this.value = x;
//   this.next = null;
// }
//
function reverseNodesInKGroups(l, k) {
  let temp = k;
  let current = l;
  const results = [];
  let temparr = [];
  while (temp && current) {
    if (current.value) {
      temparr.unshift(current.value);
    }
    current = current.next;
    temp--;
    if (temp === 0) {
      temp = k;
      results.push(...temparr);
      temparr = [];
    }
  } 
  results.push(...temparr.reverse());
  return results;
}