题目描述：

Implement the following operations of a queue using stacks.

• push(x) -- Push element x to the back of queue.
• pop() -- Removes the element from in front of queue.
• peek() -- Get the front element.
• empty() -- Return whether the queue is ...

题目描述：

Given an integer, write a function to determine if it is a power of two.

题目大意：

给定一个整数，编写函数判断它是否是2的幂。

解题思路：

如果一个整数是2的幂，那么它的二进制形式最高位为1，其余各位为0

等价于：n & (n - 1) = 0，且n > 0

Python代码：

class Solution:
    # @param {integer} n
    # @return {boolean ...

题目描述：

Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.

Note: 

You may assume k is always valid, 1 ≤ k ≤ BST's total elements.

Follow up:

What if the BST ...

题目描述：

Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times. The algorithm should run in linear time and in O(1) space.

Hint:

How many majority elements could it possibly ...

题目描述：

Given a linked list, determine if it has a cycle in it.

Follow up:

Can you solve it without using extra space?

题目大意：

给定一个链表，判断其中是否有环。

进一步思考：

你可以在不使用额外空间的条件下完成本题吗？

解题思路：

使用“快慢指针”法即可

fast指针每次向前运动两个节点，slow指针每次向前运动一个节点

如果fast和slow在链表的某处相遇，则说明链表中有环

Python代码（快慢指针）：

# Definition for singly-linked list ...