Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.

APCS 是個大學程式設計先修檢測，是個針對高中職學生的測驗，那天發現這個想說來試著寫寫看，今天寫的考題官是ˋ\網上所提供 2016-03-05 的考古題。

Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.

Validate if a given string can be interpreted as a decimal number.

You’re given strings J representing the types of stones that are jewels, and S representing the stones you have. Each character in S is a type of stone you have. You want to know how many of the stones you have are also jewels.

Given a non-empty array of digits representing a non-negative integer, plus one to the integer.

這大概是我有經驗來最神奇的面試經驗了(●▼●;)
面試時間一個小時，基本上就是就一個人寫code，另外一個人一直看著寫code..XD。想當然爾，面試結果想當然是被考官狠狠洗臉了 QAQ

（圖片來源: Heraklion Innovation Map）

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.

Given an absolute path for a file (Unix-style), simplify it. For example,
path = "/home/", => "/home"
path = "/a/./b/../../c/", => "/c"
path = "/a/../../b/../c//.//", => "/c"
path = "/a//b////c/d//././/..", => "/a/b/c"

In a UNIX-style file system, a period (‘.’) refers to the current directory, so it can be ignored in a simplified path.

Implement a trie with insert, search, and startsWith methods.