LeetCode刷题笔录 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.

这题不能像merge sort一样用extra space。做法是new一个新的链表头作为结果链表的dummy head，将两个链表按顺序插入dummy head的链表里。

public class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode p1 = l1;
        ListNode p2 = l2;
        ListNode fakeHead = new ListNode(0);
        ListNode p = fakeHead;
        
        while(p1 != null && p2 != null){
            if(p1.val <= p2.val){
                p.next = p1;
                p1 = p1.next;
            }
            else{
                p.next = p2;
                p2 = p2.next;
            }
            p = p.next;
        }
        if(p1 != null)
            p.next = p1;
        if(p2 != null)
            p.next = p2;
        return fakeHead.next;
        
    }
}