21.Merge Two Sorted Lists

Tags: Easy Linked List

Links: https://leetcode.com/problems/merge-two-sorted-lists/

---

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

---

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        if (!l1 && !l2) return nullptr;
        ListNode * dummy = new ListNode(0);
        ListNode *p = dummy;

        while (l1 && l2) {
            if (l1 -> val < l2 -> val) {
                p -> next = l1;
                p = p -> next;
                l1 = l1 -> next;
            }
            else {
                p -> next = l2;
                p = p -> next;
                l2 = l2 -> next;
            }
        }
        p -> next = l1 ? l1 : l2;

        return dummy -> next;
    }
};