Merge Two Sorted Linked Lists

MergeTwoSortedLinkedLists.java

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