445. Add Two Numbers II 两个数字相加2

You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first 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.

Follow up:
What if you cannot modify the input lists? In other words, reversing the lists is not allowed.

Example:

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


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# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
 
class Solution:
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        def list2arr(root):
            res = []
            while root:
                res.append(root.val)
                root = root.next
            return res
 
        arr1, arr2 = list2arr(l1), list2arr(l2)
        index1, index2 = len(arr1) - 1, len(arr2) - 1
        carry = 0
        root = None
        while index1 >= 0 or index2 >= 0 or carry:
            v1, v2 = 0, 0
            if index1 >= 0:
                v1 = arr1[index1]
                index1 -= 1
            if index2 >= 0:
                v2 = arr2[index2]
                index2 -= 1
 
            val = (v1 + v2 + carry)
            carry = 1 if val >= 10 else 0
 
            newNode = ListNode(val % 10)
            newNode.next = root
            root = newNode
 
        return root







posted @ 2018-02-12 22:56  xiejunzhao  阅读(191)  评论(0)  编辑  收藏  举报