mergeTwoSortedLists.py

'''
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]
'''

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next

def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:

    curr = temp = ListNode()

    while list1 and list2:
        if list1.val < list2.val: 
            curr.next = list1
            list1, curr = list1.next, list1
        else:
            curr.next = list2
            list2, curr = list2.next, list2
    curr.next = list1 or list2

    return temp.next