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2. add two numbers

admin 1月 30, 2021 0

Description

Difficulty: Easy

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 contain a single digit. Add the two numbers and return it as a linked list.

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

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

Solution

实现一个低位到高位的加法运算。注意进位即可。

# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class (object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        
        
        l_r = ListNode(0)
        head = l_r
        plus1 = 0
        
        while l1 != None or l2 != None:
            if plus1 == 0:
               l_n = ListNode(0)
               l_r.next = l_n
               l_r = l_n
            
            if l1 == None:
                l_r.val = l2.val + plus1
            elif l2 == None:
                l_r.val = l1.val + plus1
            else:
                l_r.val = l1.val + l2.val + plus1
            plus1 = 0
            
            if l_r.val >= 10:
                plus1 = 1
                l_r.val = l_r.val - 10
            if l1 != None:
                l1 = l1.next
            if l2 != None:
                l2 = l2.next
            
            if plus1 == 1:
               l_n = ListNode(1)
               l_r.next = l_n
               l_r = l_n
        return head.next