LeetCode 链表 > 21. 合并两个有序链表

21. 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

/**
 * 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) {
            return l2;
        }
        if (l2 == null) {
            return l1;
        }
        
        ListNode result = l1;
        ListNode l1Loop = l1;
        ListNode l2Loop = l2;

        if (l1Loop.val > l2Loop.val) {
            l1 = result = l2Loop;
            l2Loop = l2Loop.next;
        } else {
            l1Loop = l1Loop.next;
        }

        while (l1Loop != null) {
            while (l2Loop != null) {
                if (l1Loop.val > l2Loop.val) {
                    result.next = l2Loop;
                    result = result.next;
                    l2Loop = l2Loop.next;
                } else {
                    break;
                }
            }
            result.next = l1Loop;
            result = result.next;
            l1Loop = l1Loop.next;
        }

        while (l2Loop != null) {
            result.next = l2Loop;
            result = result.next;
            l2Loop = l2Loop.next;
        }

        return l1;

    }
}

复杂度分析

时间复杂度 : O(m+n)
空间复杂度 : O(1)