Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
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？
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
# Definition for singly-linked list ...
Given a sorted integer array without duplicates, return the summary of its ranges.
For example, given [0,1,2,4,5,7], return ["0->2","4->5","7"].
给定一组排好序且无重复的整数，返回整数范围的汇总。
例如给定数组 [0,1,2,4,5,7]， 返回 ["0->2","4->5" ...
Why don’t my numbers add up?
为什么我的数加起来对不上？
So you’ve written some absurdly simple code, say for example:
你写了一段极其简单的代码，比如：
0.1 + 0.2
and got a really unexpected result:
然后得到了一个意想不到的结果：
0.30000000000000004
Why don’t my numbers, like 0 ...
Implement a basic calculator to evaluate a simple expression string.
The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . The integer division should truncate toward zero.
You may assume that the given expression is always valid.
Some ...