LeetCoder - Merge Two Sorted Lists

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;
 *         next = null;
 *     }
 * }
 */
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.
        if(l1==null && l2==null) {
            return null;
        } else if (l1==null && l2!=null) {
            return l2;
        } else if (l1!=null && l2==null) {
            return l1;
        } else {
            ListNode head = null;
            ListNode p1 = null;
            ListNode p2 = null;
           
            if(l1.val<l2.val) {
                head = l1;
                p1 = head.next;
                p2 = l2;
            } else {
                head = l2;
                p1 = l1;
                p2 = head.next;
            }
            ListNode cur = head;
            while(p1!=null || p2!=null) {
                if(p1==null || (p2!=null && p2.val<p1.val)) {
                    cur.next = p2;
                    cur = p2;
                    p2 = p2.next;
                } else if(p2==null || (p1!=null && p1.val<=p2.val)) {
                    cur.next = p1;
                    cur = p1;
                    p1 = p1.next;
                }
            }
            return head;
        }
    }
}