# 21. 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

# Solution

Approach 1: Two pointers.

# Code (Python)

Approach 1:

# Code (C++)

Approach 1:

/**
 * 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) {
        ListNode dummyNode(0);
        ListNode *l3 = &dummyNode;
        while (l1 && l2)
        {
            if (l1->val < l2->val)
            {
                l3->next = l1;
                l1 = l1->next;
            }
            else
            {
                l3->next = l2;
                l2 = l2->next;
            }
            l3 = l3->next;
        }
        if (l1)
            l3->next = l1;
        else if (l2)
            l3->next = l2;
        return dummyNode.next;
    }
};