合并两个有序链表

将两个有序链表合并为一个新的有序链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。

示例：

输入：1->2->4, 1->3->4
输出：1->1->2->3->4->4

解决

解法一

/**
 * 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) {
  if (l1 == null) {
    return l2;
  }
  if (l2 == null) {
    return l1;
  }
  if (l1.val <= l2.val) {
    l1.next = mergeTwoLists(l1.next, l2);
    return l1;
  } else {
    l2.next = mergeTwoLists(l1, l2.next);
    return l2;
  }
};

解法二

/**
 * 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 prevHead = new ListNode(-1);
  var prevNode = prevHead;
  while (l1 != null && l2 != null) {
    if (l1.val <= l2.val) {
      prevNode.next = l1;
      l1 = l1.next
    } else {
      prevNode.next = l2;
      l2 = l2.next;
    }
    prevNode = prevNode.next;
  }
  prevNode.next = l1 ? l1 : l2;
  return prevHead.next
};

性能

Accepted

• 208/208 cases passed (72 ms)
• Your runtime beats 80.46 % of javascript submissions
• Your memory usage beats 58.61 % of javascript submissions (35.5 MB)