leetcode : Merge two sorted lists

Posted 2020-08-31 notesbuddy

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.

tag : dummy node, linked list

 

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
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 dummy = new ListNode(0);
        ListNode node = dummy;
        
        while(l1 != null && l2 != null) {
            if(l1.val > l2.val) {
                node.next = l2;
                l2 = l2.next;
            } else {
                node.next = l1;
                l1 = l1.next;
            }
            node = node.next;
        }
        if(l1 != null) {
            node.next = l1;
        }
        if(l2 != null) {
            node.next = l2;
        }
        return dummy.next;
        
    }
}