Leet Code 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

/** * 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) {// Note: The Solution object is instantiated only once and is reused by each test case.ListNode p,q,r,head;if(l1 == null){return l2;}if(l2 == null){return l1;}p = l1;q = l2;head = null;if(p.val <= q.val){head = p;p = p.next;}else{head = q;q = q.next;}r = head;while(p != null && q != null){if(p.val <= q.val){r.next = p;r = p;p = p.next;}else{r.next = q;r = q;q = q.next;}}while(q != null){r.next = q;r = q;q = q.next;}while(p != null){r.next = p;r = p;p = p.next;}return head;}}