leetcode: 21. Merge Two Sorted Lists

Difficulty

Easy

Description

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.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

Solution

/**
 * 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 ret = new ListNode(0);
		ListNode head = ret;
		while (l1 != null && l2 != null)
		{
			if (l1.val <= l2.val)
			{
				head.next = l1;
				l1 = l1.next;
			} else {
				head.next = l2;
				l2 = l2.next;
			}
            
            head = head.next;
		}
        
		if (l1 != null)
		{
			head.next = l1;
		} else if (l2 != null)
		{
			head.next = l2;
		} 

		return ret.next;
    }
}