In 91

上回邀請朋友一起來進行 pair programming，隨機挑了一個 Codewars 的題目來練習：Mumbling。

題目描述：

Codewars 上隨機挑到的題目：Number of People in the Bus

Codewars 上隨機挑到的一個題目：Buying A Car

Codewars 上的 kata: Next bigger number with the same digits

You have to create a function that takes a positive integer number and returns the next bigger number formed by the same digits:
f(12) == 21
f(513) == 531
f(2017) == 2071

If no bigger number can be composed using those digits, return -1:
f(9) == -1
f(111) == -1
f(531) == -1

用 TDD 來練習完成 leet code 的第 219 題，題目描述如下。

Given an array of integers and an integer k, find out whether there are two distinct indices i and j in the array such that nums[i] = nums[j] and the absolute difference between i and j is at most k.