###### tags: `Linked List`, `Recursion`

# LeetCode 21.Merge Two Sorted Lists

You are given the heads of two sorted linked lists ```list1``` and ```list2```.

Merge the two lists in a one sorted list. The list should be made by splicing together the nodes of the first two lists.

Return the head of the merged linked list.


>Example 1:

Input: list1 = [1,2,4], list2 = [1,3,4]
Output: [1,1,2,3,4,4]

>Example 2:

Input: list1 = [], list2 = []
Output: []

>Example 3:

Input: list1 = [], list2 = [0]
Output: [0]

### Constraints:

- The number of nodes in both lists is in the range ```[0, 50]```.
- $-100 <= Node.val <= 100$
- Both ```list1``` and ```list2``` are sorted in non-decreasing order.
---
### Idea:
>
### Solution:

Python:

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
        merge = ListNode()
        cursor = merge
        while list1 and list2:
            if list1.val <= list2.val:
                cursor.next = list1
                list1 = list1.next
            else:
                cursor.next = list2
                list2 = list2.next
            cursor=cursor.next
        if list1:
            cursor.next = list1
        else:
            cursor.next = list2
        return merge.next

C++