LeetCode-21 Merge Two Sorted Lists Solution (with Java)

1. Description: 

2.Solutions:

/**
 * Created by sheepcore on 2019-05-10
 * 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) {
        ListNode head = new ListNode(-1);
        ListNode p = l1, q = l2, tail = head;
        while (p != null && q != null){
            if(p.val <= q.val){
                tail.next  = p;
                p = p.next;
                tail = tail.next;
            } else{
                tail.next = q;
                q = q.next;
                tail = tail.next;
            }
        }
        if(p != null)
            tail.next = p;
        if(q != null)
            tail.next = q;
        return head.next;
    }
}