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leetcode no 21 merge two sorted lists

admin 11月 11, 2020 0

1. 题目

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.

2. 思路

注意不要开辟额外空间就好。


 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class  {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode result = new ListNode(0);
        ListNode pListNode = result;
        while(l1 != null || l2 != null){
        	if(l1 != null && l2 != null){
        		if(l1.val < l2.val){
        			pListNode.next = l1;
        			l1 = l1.next;
        		}else{
        			pListNode.next = l2;
        			l2 = l2.next;
        		}
        		pListNode = pListNode.next;
        	}else if(l1 == null){
        		pListNode.next = l2;
        		break;
        	}else if(l2 == null){
        		pListNode.next = l1;
         		break;
            }
        }
        return result.next;
    }
}