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.
Example:
Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4
详见：https://leetcode.com/problems/merge-two-sorted-lists/description/
Java实现：
非递归：
/**
* 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;
}
if(l1==null&&l2==null){
return null;
}
ListNode head=new ListNode(-1);
ListNode cur=head;
while(l1!=null&&l2!=null){
if(l1.val<l2.val){
cur.next=l1;
l1=l1.next;
}else{
cur.next=l2;
l2=l2.next;
}
cur=cur.next;
}
cur.next=l1==null?l2:l1;
return head.next;
}
}
递归：
/**
* 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;
}
if(l1==null){
return l2;
}
if(l2==null){
return l1;
}
ListNode head=null;
if(l1.val<l2.val){
head=l1;
head.next=mergeTwoLists(l1.next,l2);
}else{
head=l2;
head.next=mergeTwoLists(l1,l2.next);
}
return head;
}
}