【leetcode系列】【算法】【中等】两数相加 II

题目：

题目链接： https://leetcode-cn.com/problems/add-two-numbers-ii/

解题思路：

利用栈后进先出的特性，把两个链表放入栈中，然后对栈进行遍历，把数字相加，生成新的链表返回

代码实现：

# 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:
        stack_l1 = []
        stack_l2 = []
        while l1:
            stack_l1.append(l1.val)
            l1 = l1.next
            
        while l2:
            stack_l2.append(l2.val)
            l2 = l2.next
            
        m, n = len(stack_l1), len(stack_l2)
        if m < n:
            m, n = n, m
            stack_l1, stack_l2 = stack_l2, stack_l1
            
        is_add = 0
        head = ListNode(0)
        while stack_l1:
            num1 = num2 = 0
            num1 = stack_l1[-1]
            stack_l1.pop()
            if stack_l2:
                num2 = stack_l2[-1]
                stack_l2.pop()
                
            curr_num = num1 + num2 + is_add
            if curr_num >= 10:
                curr_num -= 10
                is_add = 1
            else:
                is_add = 0
                
            curr_node = ListNode(curr_num)
            curr_node.next = head.next
            head.next = curr_node
            
        if is_add == 1:
            curr_node = ListNode(1)
            curr_node.next = head.next
            head.next = curr_node
        return head.next