合并两个有序链表 Merge Two Sorted Lists

题目

给定一个只包括 '('，')'，'{'，'}'，'['，']' 的字符串，判断字符串是否有效。

以下为详细说明：

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

思路&题解

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {

    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null) {
            if (l2 == null) {
                return l1;
            } else {
                return l2;
            }
        }
        if (l2 == null) {
            return l1;
        }
        ListNode result = null;
        ListNode top = l1.val < l2.val ? l1 : l2;
        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                if (result == null) {
                    result = l1;
                } else {
                    result.next = l1;
                    result = result.next;
                }
                l1 = l1.next;
            } else {
                if (result == null) {
                    result = l2;
                } else {
                    result.next = l2;
                    result = result.next;
                }
                l2 = l2.next;
            }
        }
        if (l1 == null) {
            result.next = l2;
        } else {
            result.next = l1;
        }
        return top;
    }
}

知识点分析