leetcode No.2 adding two numbers (implemented to python3)

source

https://leetcode-cn.com/problems/add-two-numbers/

Title Description

We are given two non-empty list is used to represent two non-negative integer. Where their respective bits are stored in reverse order of the way, and they each node can store only one digit.

If we add up these two numbers, it will return a new list and to represent them.

You can assume that in addition to the numbers 0, these two numbers will not begin with 0.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Cause: 342 + 465 = 807

Code

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

class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        n = l1.val + l2.val 
        l3 = ListNode(n % 10)
        l3.next = ListNode(n // 10)
        p1 = l1.next 
        p2 = l2.next 
        p3 = l3 
        while True:
            if p1 and p2:
                total = p1.val + p2.val + p3.next.val 
                p3.next.val = total % 10
                p3.next.next = ListNode(total // 10)
                p1 = p1.next 
                p2 = p2.next
                p3 = p3.next
            elif p1 and not p2:
                total = p1.val + p3.next.val 
                p3.next.val = total % 10
                p3.next.next = ListNode(total // 10)
                p1 = p1.next 
                p3 = p3.next
            elif not p1 and p2:
                total = p2.val + p3.next.val 
                p3.next.val = total % 10
                p3.next.next = ListNode(total // 10) 
                p2 = p2.next
                p3 = p3.next
            else:
                if p3.next.val == 0:
                    p3.next = None
                break
        return l3

The core idea is to set a new variable l3, to determine whether it is greater than 10, then consider the four cases,

P1 P2同时存在，
P1存在，P2不存在，
P2存在，P1不存在，
P1 P2都不存在

Then after the next node is constantly updated calculated, the final output variable.