[LeetCode-Java]21. Merge Two Sorted Lists

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.

解：链表的基本操作。

public class Solution {
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {

ListNode head = null;
ListNode temp = null;//存放已排序部分的最后一个位置

if (l1 == null) return l2;
if (l2 == null) return l1;

if (l1.val <= l2.val){
head = l1;
}else {
head = l2;
}

//比较移动l1和l2
while (l1!= null && l2 != null){

if (l1.val <= l2.val){
if (temp != null) temp.next = l1;
temp = l1;  //temp始终指向两者之中最小的那个
l1 = l1.next;
}else {
if (temp != null) temp.next = l2;
temp = l2;
l2 = l2.next;
}

}

if (l1 == null) temp.next = l2;
if (l2 == null) temp.next = l1;

return head;

}

}