21. Merge Two Sorted Lists

/**
 * 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) {
        if(l1 == null && l2==null) return null;
        if(l1 == null) return l2;
        if(l2 == null) return l1;
        ListNode ans = new ListNode(0);
        ListNode temp = ans;
        ListNode temp2 = ans;
        while(l1 !=null || l2!=null) {
            if(l1!=null && l2!=null) {
                if(l1.val > l2.val) {
                    temp.val = l2.val; 
                    l2 = l2.next;
                }else {
                    temp.val = l1.val; 
                    l1 = l1.next;
                }
            }else {
                if(l1 == null) {
                    temp.val = l2.val; 
                    l2 = l2.next;
                    temp.next = l2;
                    break;
                }else if(l2 == null) {
                    temp.val = l1.val; 
                    l1 = l1.next;
                    temp.next = l1;
                    break;
                }
            }
            temp.next = new ListNode(0);
            temp = temp.next;
        }
        return ans;
    }
}