21. Merge Two Sorted Lists

Problem

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

Solution

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var mergeTwoLists = function(l1, l2) {
  var head = new ListNode(0);
  var now = head;
  var p1 = l1;
  var p2 = l2;
  while (p1 || p2) {
    if (p1 === null || (p2 !== null && p2.val < p1.val)) {
      now.next = p2;
      p2 = p2.next;
    } else {
      now.next = p1;
      p1 = p1.next;
    }
    now = now.next;
  }
  return head.next;
};

Explain:

nope.

Complexity:

• Time complexity : O(m+n).
• Space complexity : O(m+n).