LC 合并两个有序链表

将两个升序链表合并为一个新的 升序 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。

【代码】

/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode() {} * ListNode(int val) { this.val = val; } * ListNode(int val, ListNode next) { this.val = val; this.next = next; } * } */
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
            //下面4行是空判断
            if (l1 == null)
                return l2;
            else if (l2 == null)
                return l1;

            ListNode head = new ListNode();
            ListNode curr = head;

            while (l1 != null && l2 !=null)
            {
                if (l1.val < l2.val)        //谁小谁先入
                {
                    curr.next = l1;
                    l1 = l1.next;
                }
                else
                {
                    curr.next = l2;
                    l2 = l2.next;
                }
                curr = curr.next;
            }
            curr.next = l1 == null ? l2:l1;    //把不为空的链表挂到后面
            return head.next;
    }
}