【刷题日记】leetcode2——Add Two Numbers

本文介绍了一种解决链表加法问题的方法,即两个非空链表表示的非负整数相加,并返回结果作为新的链表。通过遍历链表节点并考虑进位情况,实现了高效的算法,最后讨论了代码的时间和空间复杂度。

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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 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.

Example:

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


  • 注意标志位
  • 注意每次相加都要调整标志位为0或者1
  • 注意链表遍历完毕后如果标志位为1需要增加一个结点。
# 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:
        p1 = l1
        p2 = l2
        preHead = ListNode(-1)
        p3 = preHead
        flag = 0
        while p1 and p2:
            result = p1.val+p2.val+flag
            if result >=10:
                result %=10
                flag =1
            else:
                flag = 0
            newNode = ListNode(result)
            p3.next = newNode
            p3 = p3.next
            p1 = p1.next
            p2 = p2.next
        if p1:
            while p1:
                result = p1.val+flag
                if result >= 10:
                    result %= 10
                    flag =1
                else:
                    flag =0
                newNode = ListNode(result)
                p3.next = newNode
                p3 = p3.next
                p1 = p1.next
        if p2:
            while p2:
                result = p2.val+flag
                if result >= 10:
                    result %= 10
                    flag =1
                else:
                    flag = 0
                newNode = ListNode(result)
                p3.next = newNode
                p3 = p3.next
                p2 = p2.next
        if flag ==1:
            newNode = ListNode(1)
            p3.next = newNode
        return preHead.next
            

result

Runtime: 72 ms, faster than 91.85% of Python3 online submissions for Add Two Numbers.
Memory Usage: 13.9 MB, less than 5.67% of Python3 online submissions for Add Two Numbers.

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