今天做了三道LeetCode上的简单题目，每道题都是用c++和Python两种语言写的。由于c++版的代码网上比較多。所以就仅仅分享一下Python的代码吧，刚学完Python的基本的语法，做做LeetCode的题目还是不错的，对以后找工作面试也有帮助！

刚開始就从AC率最高的入手吧！

1.Given an array of integers, every element appears twice except for one. Find that single one.

Note:

Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

開始纠结于线性时间复杂度和不要额外的存储空间。思路是遍历一遍数组。想象成翻硬币。碰到一次就翻面，再碰到就翻回来了。剩下的那个仍是背面的就是仅仅出现一次的。可是这样的思路就势必要有额外的存储空间。后来看了别人的思路，原来所有异或就能够了。由于A XOR A =0，0 XOR any = any。简单多了。

class Solution:    # @param A, a list of integer    # @return an integer    def singleNumber(self, A):        result = 0        for i in A:            result = result ^ i        return result

2.Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

递归寻找左子树和右子树的深度，取二者较大的，再加上根的深度1。即为答案。

# Definition for a  binary tree node# class TreeNode:#     def __init__(self, x):#         self.val = x#         self.left = None#         self.right = Noneclass Solution:    # @param root, a tree node    # @return an integer    def maxDepth(self, root):        if root is None:            return 0        else:            return max(self.maxDepth(root.left),self.maxDepth(root.right))+1