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21. Merge Two Sorted Lists

Question

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 l3 = new ListNode(0);
        ListNode dummyHead = l3;
        while (l1 != null && l2 != null) {
            if (l1.val <= l2.val) {
                l3.next = l1;
                l1 = l1.next;
            } else {
                l3.next = l2;
                l2 = l2.next;
            }
           
            l3 = l3.next;
        }
        
        if (l1==null){
            l3.next = l2;
        }else {
            l3.next  =l1;
        }

        return dummyHead.next;

    }
}
Execution time: 2 ms, defeated 96.19% of users in the Java submission of Merge Two Sorted Lists
Memory consumption: 34.9 MB, defeated 94.47% of users in the Java submission of Merge Two Sorted Lists

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