add two problems

%% Cell type:markdown id: tags:

# My LeetCode

## 1. twoSum

## 1. 两数之和

以下的方案不能通过 LeetCode 提交，可能原因是全局变量的引入。

%% Cell type:code id: tags:

``` python

class Solution:

    def twoSum(self, nums, target):

        for i in range(len(nums)):

            if target - nums[i] in nums:

                return [i, nums.index(target-nums[i])]

# test

if __name__ == '__main__':

    s = Solution()

    print(s.twoSum([2,8,11,7,15],9))

```

%% Output

    [0, 3]

%% Cell type:markdown id: tags:

## 2. addTwoNumbers

## 2. 两数相加

以下我的方法是针对 List 而非 ListNode. orz

%% Cell type:code id: tags:

``` python

class Solution:

    def addTwoNumbers(self, l1, l2):

        num1 = 0

        for i in range(len(l1)):

            num1 = num1 + l1[i] * 10**(i)

        num2 = 0

        for j in range(len(l2)):

            num2 = num2 + l2[j] * 10**(j)

        nnum = num1+num2

        return [int(x) for x in str(nnum)[::-1]]

if __name__ == '__main__':

    s = Solution()

    print(s.addTwoNumbers([1,2,3],[0,8,4]))

```

%% Output

    [1, 0, 8]

%% Cell type:markdown id: tags:

# 7. 整数反转

使用切片 `[::-1]` 来实现反转整数，最后判定大小溢出。

%% Cell type:code id: tags:

``` python

class Solution:

    def reverse(self, x: int) -> int:

        if x>=0:

            ans = int(str(x)[::-1])

        else:

            ans = -int(str(x)[:0:-1])

        if -2**31 <= ans < 2**31:

            return ans

        else:

            return 0

if __name__ == '__main__':

    s = Solution()

    print(s.reverse(-1236469))

```

%% Output

    -9646321

%% Cell type:code id: tags:

``` python

```