[21][Easy] Merge Two Sorted Lists.py

# 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, l2):
        start = current = ListNode()
        while l1 and l2:
            if l1.val < l2.val:
                current.next = l1
                l1 = l1.next
            else:
                current.next = l2
                l2 = l2.next
            current = current.next
        current.next = l1 or l2
        return start.next