0147-insertion-sort-list.js

/**
 * 147. Insertion Sort List
 * https://leetcode.com/problems/insertion-sort-list/
 * Difficulty: Medium
 *
 * Given the head of a singly linked list, sort the list using insertion sort, and
 * return the sorted list's head.
 *
 * The steps of the insertion sort algorithm:
 * - Insertion sort iterates, consuming one input element each repetition and growing
 *   a sorted output list.
 * - At each iteration, insertion sort removes one element from the input data, finds
 *   the location it belongs within the sorted list and inserts it there.
 * - It repeats until no input elements remain.
 *
 * The following is a graphical example of the insertion sort algorithm. The partially
 * sorted list (black) initially contains only the first element in the list. One
 * element (red) is removed from the input data and inserted in-place into the sorted
 * list with each iteration.
 */

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var insertionSortList = function(head) {
  const result = new ListNode(0);

  while (head) {
    const tail = head;
    let current = result;
    head = head.next;

    while (current) {
      if (!current.next || tail.val <= current.next.val) {
        [current.next, tail.next] = [tail, current.next];
        break;
      }
      current = current.next;
    }
  }

  return result.next;
};