# [LC] 21. Merge Two Sorted Lists

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 = 
Output: 
```

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.

## Approach

Easy question. Just iterate both lists and connect to the temporary head list. If l1 or l2 is done, keep doing there is no remain node.

``````# 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, l1: ListNode, l2: ListNode) -> ListNode:
combined = ListNode(0)
while l1 and l2:
if l1.val < l2.val:
combined.next = l1
l1, combined = l1.next, combined.next
else:
combined.next = l2
l2, combined = l2.next, combined.next

while l1:
combined.next = l1
l1, combined = l1.next, combined.next

while l2:
combined.next = l2
l2, combined = l2.next, combined.next