LeetCode——2.两数相加

# 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:
        
        if not l1:
            return l2
        if not l2:
            return l1
        
        #主要还是维护一个进位
        carry = 0
        dummpy = ListNode(0)
        pre = dummpy
        while l1 or l2:
            x = l1.val if l1 else 0
            y = l2.val if l2 else 0

            Sum = x+y+carry
            carry = Sum//10

            node = ListNode(Sum%10)
            pre.next = node
            pre = pre.next
            if l1:
                l1 = l1.next
            if l2:
                l2 = l2.next
        if carry>0:
            pre.next = ListNode(carry)
        
        return dummpy.next

• 两个链表中的数字相加维护一个进位即可
• 还要处理最后一个进位