2. 两数相加

思路

1. 两个结点的值相加除以10，将结果的整数部分存储至新链表里（prelist），商加入两个链表下一个结点的值相加的运算中
2. 若某个链表结点为None（走到尾部）则设置结点值为0来进行计算
3. 链表都遍历结束后，若还有商（即最后一个结点时，相加值>10,需要进位）（即 s!=0）,将商也加入新链表中
   代码

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):def addTwoNumbers(self, l1, l2):""":type l1: ListNode:type l2: ListNode:rtype: ListNode"""if l1 is None:if l2 is None:return Noneelse:return l2else:if l2 is None:return l1prelist = ListNode(-1)pre =prelists = 0while l1 or l2:if l1:t1=l1.valelse:t1 = 0if l2:t2=l2.valelse:t2 = 0cur=t1+t2+ss=cur//10cur = cur%10pre.next =ListNode(cur)pre=pre.nextif l1:l1=l1.nextif l2:l2=l2.nextif s != 0:pre.next=ListNode(s)return prelist.next