LeetCode 21. Merge Two Sorted Lists 两个有序列表合成一个

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.

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/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
ListNode newList = new ListNode(0);
ListNode move = newList;
while(l1!=null&&l2!=null){
if(l1.val>=l2.val){
ListNode NewNode = new ListNode(l2.val);
move.next = NewNode;
move = move.next;
l2 = l2.next;
}
else{
ListNode NewNode = new ListNode(l1.val);
move.next = NewNode;
move = move.next;
l1 = l1.next;
}
}
if(l1==null){
move.next = l2;
}
if(l2==null){
move.next = l1;
}
return newList.next;
}
}

还是锁住链表头部，让后面ListNode移动的问题

比较精简的方法（递归）：

public ListNode mergeTwoLists(ListNode l1, ListNode l2){
if(l1 == null) return l2;
if(l2 == null) return l1;
if(l1.val < l2.val){
l1.next = mergeTwoLists(l1.next, l2);
return l1;
} else{
l2.next = mergeTwoLists(l1, l2.next);
return l2;
}
}