leetcode/work/1/Medium/Linked List/2.add-two-numbers.py

"""
2. Add Two Numbers
Difficulty: Medium
https://leetcode.com/problems/add-two-numbers/

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You are given two non-empty linked lists representing two
non-negative integers. The digits are stored in reverse order, and
each of their nodes contains a single digit. Add the two numbers and
return the sum as a linked list.

You may assume the two numbers do not contain any leading zero,
except the number 0 itself.



Example 1:

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.

Example 2:

Input: l1 = [0], l2 = [0]
Output: [0]

Example 3:

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output: [8,9,9,9,0,0,0,1]



Constraints:

        • The number of nodes in each linked list is in the range [1, 100].

        • 0 <= Node.val <= 9

• It is guaranteed that the list represents a number that does not
have leading zeros.
"""


# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def addTwoNumbers(
        self, l1: Optional[ListNode], l2: Optional[ListNode]
    ) -> Optional[ListNode]:

        dummy = ListNode()
        carry = 0
        curr = dummy
        while l1 or l2 or carry:
            s = (l1.val if l1 else 0) + (l2.val if l2 else 0) + carry
            carry, val = divmod(s, 10)

            curr.next = ListNode(val)
            curr = curr.next

            l1 = l1.next if l1 else None
            l2 = l2.next if l2 else None

        return dummy.next