# 档案日期2015的27

## 题目描述：

Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w ...

## 题目描述：

Given a linked list, return the node where the cycle begins. If there is no cycle, return null.

Can you solve it without using extra space?

## 题目描述：

Given a singly linked list, determine if it is a palindrome.

Could you do it in O(n) time and O(1) space?

## 解题思路：

1). 使用快慢指针寻找链表中点

2). 将链表的后半部分就地逆置 ...

## 题目描述：

Given an integer n, count the total number of digit 1 appearing in all non-negative integers less than or equal to n.

For example:

Given n = 13,

Return 6, because digit 1 occurred in the following numbers: 1, 10 ...

## 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 ...