leetcode 合并两个有序列表

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。 

/**
 * 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&&l2==null){
            return null;
        }
        ListNode l3 = null;
        ListNode head = null;
        while(l1!=null||l2!=null){
            int temp = 0 ;
            if(l1!=null&&l2!=null){
                if(l1.val<=l2.val){
                    temp=l1.val;
                    l1=l1.next;
                }else{
                    temp=l2.val;
                    l2=l2.next;
                }
            }
            else if(l1==null){
                temp=l2.val;
                l2=l2.next;
            }
            else if(l2==null){
                temp=l1.val;
                l1=l1.next;
            }
            ListNode next = new ListNode(temp);
            if(l3==null){
                l3=next;
                head =l3;
            }else{
                l3.next=next;
                l3=l3.next;
            }
        }
        l3.next=null;
        return head;
    }
}