Leetcode刷题记录——2. 两数相加

我实现了两种方法
1、借助字符串和加法：

# 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:
        stra = ''
        strb = ''
        while l1 is not None:
            stra = str(l1.val) + stra
            l1 = l1.next
        while l2 is not None:
            strb = str(l2.val) + strb
            l2 = l2.next
        res = str(int(stra) + int(strb))
        res = res[::-1]
        length = len(res)
        rootnode = ListNode(int(res[0]))
        if length == 1:
            return rootnode
        for i in range(length):
            if i == 0:
                tempnode = rootnode
            else:
                tempnode.next = ListNode(int(res[i]))
                tempnode = tempnode.next
        return rootnode

2、逐位相加法

# 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:        
        temp = 0
        toreturn = []#存放结果中的每一位数字
        while l1 is not None and l2 is not None:
            temp_res = l1.val + l2.val + temp
            temp = 0
            if temp_res >= 10:
                temp_res -= 10
                temp = 1
            toreturn.append(temp_res)
            l1 = l1.next
            l2 = l2.next
        
        if l1 is None and l2 is not None:
            while l2 is not None:
                temp_res = l2.val+temp
                if temp_res >= 10:
                    toreturn.append(temp_res-10)
                    temp = 1 
                else:
                    toreturn.append(temp_res)
                    temp = 0
                l2 = l2.next
            if temp == 1:
                toreturn.append(1)
            return self.list2listnode(toreturn)
        if l2 is None and l1 is not None:
            while l1 is not None:
                temp_res = l1.val + temp
                if temp_res >= 10:
                    toreturn.append(temp_res-10)
                    temp = 1
                else:
                    toreturn.append(temp_res)
                    temp = 0
                l1 = l1.next
            if temp == 1:
                toreturn.append(1)
            return self.list2listnode(toreturn)
        if l1 is None and l2 is None:
            if temp == 1:
                toreturn.append(temp)
            return self.list2listnode(toreturn)

    def list2listnode(self,input_list):
        length = len(input_list)
        if length == 1:
            return ListNode(input_list[0])
        for i in range(length-1):
            if i == 0:
                rootnode = ListNode(input_list[0])
                tempnode = ListNode(input_list[1])
                rootnode.next = tempnode
            else:
                tempnode.next = ListNode(input_list[i+1])
                tempnode = tempnode.next
        return rootnode