Merge two sorted linked lists and return it as a new sorted list. The new list should be made by splicing together the nodes of the first two lists.
Example 1:
Input: l1 = [1,2,4], l2 = [1,3,4] Output: [1,1,2,3,4,4]
Example 2:
Input: l1 = [], l2 = [] Output: []
Example 3:
Input: l1 = [], l2 = [0] Output: [0]
Constraints:
[0, 50].-100 <= Node.val <= 100l1 and l2 are sorted in non-decreasing order.合并两个有序链表。
给两个有序链表，请将两个链表merge，并且输出的链表也是有序的。
时间O(m + n)，两个链表的长度
空间O(1)
思路:
用一个dummy node去遍历两个链表，然后比较两者的node.val。
解法类似归并排序的merge过程
merge K个链表
class Solution {
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
if(l1==null&&l2==null){
return null;
}
ListNode p1=l1;
ListNode p2=l2;
ListNode p3=new ListNode(0);
ListNode cur=p3;
while(p1!=null && p2!=null){
if(p1.val<p2.val){
cur.next=p1;
p1=p1.next;
}else{
cur.next=p2;
p2=p2.next;
}
cur=cur.next;
}
while(p1!=null){
cur.next=p1;
cur=cur.next;
p1=p1.next;
}
while(p2!=null){
cur.next=p2;
cur=cur.next;
p2=p2.next;
}
return p3.next;
}
}
原文：https://www.cnblogs.com/iwyc/p/15203049.html