Leetcode(21)合并两个有序链表

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

关键技巧：注意current的设置顺序，又不改变l1,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) {
                //注意顺序，如何设置当前节点又不改变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;
        }
        return mergeListNode.next;
    }
}