Leetcode(21) merges two ordered lists

Merge Two Sorted Lists

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
Copy the code

Key technique: pay attention to the setting order of current without changing L1 and L2

/** * 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 mergeListNode = new ListNode(-1);
        ListNode current = mergeListNode;
        while(l1 ! =null&& l2 ! =null) {
            if (l1.val > l2.val) {
                // Notice the order, how to set the current node without changing one,two
                current.next = l2;
                current = current.next;
                l2 = l2.next;
            } else{ current.next = l1; current = current.next; l1 = l1.next; }}if(l1 ! =null) {
            current.next = l1;
        }
        if(l2 ! =null) {
            current.next = l2;
        }
        returnmergeListNode.next; }}Copy the code