Merge Two Sorted Lists | Leetcode

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.

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Solution: First get the head node as we will return that at the end. Then go through the nodes in l1 and l2, always adding the smaller node first.

/**
 * 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 head;
        if (l1.val < l2.val) {
            head = l1;
            l1 = l1.next;
        } else {
            head = l2;
            l2 = l2.next;
        }
        
        ListNode curr = head;
        while (true) {
            if (l1 == null) {
                curr.next = l2;
                break;
            }
            if (l2 == null) {
                curr.next = l1;
                break;
            }
            if (l1.val < l2.val) {
                curr.next = l1;
                l1 = l1.next;
            } else {
                curr.next = l2;
                l2 = l2.next;
            }
            curr = curr.next;
        }
        
        return head;
    }
}