兩數(shù)相加
給你兩個(gè) 非空 的鏈表,表示兩個(gè)非負(fù)的整數(shù)。它們每位數(shù)字都是按照 逆序 的方式存儲(chǔ)的,并且每個(gè)節(jié)點(diǎn)只能存儲(chǔ) 一位 數(shù)字。
請(qǐng)你將兩個(gè)數(shù)相加,并以相同形式返回一個(gè)表示和的鏈表。
你可以假設(shè)除了數(shù)字 0 之外,這兩個(gè)數(shù)都不會(huì)以 0 開(kāi)頭。

示例 1:
輸入:l1 = [2,4,3], l2 = [5,6,4]
輸出:[7,0,8]
解釋?zhuān)?42 + 465 = 807.
示例 2:
輸入:l1 = [0], l2 = [0]
輸出:[0]
示例 3:
輸入:l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
輸出:[8,9,9,9,0,0,0,1]
思路:
1.創(chuàng)建一個(gè)新鏈表,新鏈表的頭部先設(shè)置為l1頭部和l2頭部之和。
2.遍歷兩個(gè)鏈表,只要有一個(gè)還沒(méi)有遍歷完就繼續(xù)遍歷
3.每次遍歷生成一個(gè)當(dāng)前節(jié)點(diǎn)cur的下一個(gè)節(jié)點(diǎn),其值為兩鏈表對(duì)應(yīng)節(jié)點(diǎn)的和再加上當(dāng)前節(jié)點(diǎn)cur產(chǎn)生的進(jìn)位
4.更新進(jìn)位后的當(dāng)前節(jié)點(diǎn)cur的值
5.循環(huán)結(jié)束后,因?yàn)槭孜豢赡墚a(chǎn)生進(jìn)位,因此如果cur.val是兩位數(shù)的話,新增一個(gè)節(jié)點(diǎn)
6.返回頭節(jié)點(diǎn)
由題目注釋可以看出listNode這個(gè)類(lèi)是用來(lái)創(chuàng)建鏈表的,默認(rèn)next=None,val=0.
Definition for singly-linked list.
class ListNode:
def init(self, val=0, next=None):
self.val = val
self.next = next
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
class Solution:
def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
head = ListNode(l1.val+l2.val)
current = head
while l1.next or l2.next:
l1 = l1.next if l1.next else ListNode()
l2 = l2.next if l2.next!=None else ListNode()
current.next = ListNode(l1.val+l2.val+current.val//10)
current.val = current.val%10
current = current.next
if current.val >= 10:
current.next = ListNode(current.val//10)
current.val = current.val%10
return head
改進(jìn)改進(jìn):增加了空間復(fù)雜度。本以為一方為None后直接把另一個(gè)鏈表連上就ok了。然后,就打臉了。

然后又加了while
> [9999]
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
class Solution:
def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
head = ListNode(l1.val+l2.val)
current = head
while l1.next and l2.next:
l1 = l1.next
l2 = l2.next
current.next = ListNode(l1.val+l2.val+current.val//10)
current.val = current.val%10
current = current.next
if l1.next == None and l2.next :
while l2.next:
l2 = l2.next
current.next= ListNode(l2.val+current.val//10)
current.val = current.val%10
current = current.next
current.next = l2.next
elif l2.next == None and l1.next:
while l1.next:
l1 = l1.next
current.next= ListNode(l1.val+current.val//10)
current.val = current.val%10
current = current.next
current.next = l2.next
if current.val >= 10:
current.next = ListNode(current.val//10)
current.val = current.val%10
return head

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