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21. Merge Two Sorted Lists

Easy

Merge two sorted linked lists and return it as a sorted list. The list should be made by splicing together the nodes of the first two lists.

Example 1:

Input: l1 = [1,2,4], l2 = [1,3,4]

Output: [1,1,2,3,4,4]

Example 2:

Input: l1 = [], l2 = []

Output: []

Example 3:

Input: l1 = [], l2 = [0]

Output: [0]

Constraints:

• The number of nodes in both lists is in the range [0, 50].
• -100 <= Node.val <= 100
• Both l1 and l2 are sorted in non-decreasing order.

Solution

using LeetCodeNet.Com_github_leetcode;

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int val=0, ListNode next=null) {
 *         this.val = val;
 *         this.next = next;
 *     }
 * }
 */
public class Solution {
    public ListNode MergeTwoLists(ListNode l1, ListNode l2) {
        ListNode list = new ListNode(-1);
        ListNode head = list;

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

        return head.next;
    }
}

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