21. 合并两个有序链表-LeetCode

/**
 * 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 head=new ListNode(-1);
        ListNode tmp=head;       
        while(l1!=null&&l2!=null)
        {
        	if(l1.val<=l2.val)
        	{
        		tmp.next=l1;
        		tmp=tmp.next;
        		l1=l1.next;
        	}
        	else 
        	{
        		tmp.next=l2;
        		tmp=tmp.next;
        		l2=l2.next;
        	}
        }
        while(l1!=null)   ///将剩余的添加上
        {
        	tmp.next=l1;
        	tmp=tmp.next;
    		l1=l1.next;
        }
        while(l2!=null)     ////将剩余的添加上
        {
        	tmp.next=l2;
        	tmp=tmp.next;
    		l2=l2.next;
        }
        return head.next;
    }
}