Java版排列组合工具类 - Java Permutation and Combination Tools

( All code listed in this article is included in my personal lib, and the repo is hosted at: https://github.com/raistlic/LibRaistCommon )

先上用法示例代码：

问题一： 有三个字符串 "a", "b", "c"，进行排列，列出共有多少种排列方式

运行效果：

run:
===== demo permutation :
[a, b, c]
[a, c, b]
[b, a, c]
[b, c, a]
[c, a, b]
[c, b, a]
BUILD SUCCESSFUL (total time: 0 seconds)

问题二： 从五个数 1, 2, 3, 4, 5 中任取 3 个数，列出共有多少种取法

运行效果：
run:
===== demo combination :
[1, 2, 3]
[1, 2, 4]
[1, 2, 5]
[1, 3, 4]
[1, 3, 5]
[1, 4, 5]
[2, 3, 4]
[2, 3, 5]
[2, 4, 5]
[3, 4, 5]
BUILD SUCCESSFUL (total time: 0 seconds)

问题三： 从五个数 1, 2, 3, 4, 5 中任取 3 个数进行排列，列出共有多少种排列方式

运行效果：

run:
===== demo both :
[1, 2, 3]
[1, 3, 2]
[2, 1, 3]
[2, 3, 1]
[3, 1, 2]
[3, 2, 1]
[1, 2, 4]
[1, 4, 2]
[2, 1, 4]
[2, 4, 1]
[4, 1, 2]
[4, 2, 1]
[1, 2, 5]
[1, 5, 2]
[2, 1, 5]
[2, 5, 1]
[5, 1, 2]
[5, 2, 1]
[1, 3, 4]
[1, 4, 3]
[3, 1, 4]
[3, 4, 1]
[4, 1, 3]
[4, 3, 1]
[1, 3, 5]
[1, 5, 3]
[3, 1, 5]
[3, 5, 1]
[5, 1, 3]
[5, 3, 1]
[1, 4, 5]
[1, 5, 4]
[4, 1, 5]
[4, 5, 1]
[5, 1, 4]
[5, 4, 1]
[2, 3, 4]
[2, 4, 3]
[3, 2, 4]
[3, 4, 2]
[4, 2, 3]
[4, 3, 2]
[2, 3, 5]
[2, 5, 3]
[3, 2, 5]
[3, 5, 2]
[5, 2, 3]
[5, 3, 2]
[2, 4, 5]
[2, 5, 4]
[4, 2, 5]
[4, 5, 2]
[5, 2, 4]
[5, 4, 2]
[3, 4, 5]
[3, 5, 4]
[4, 3, 5]
[4, 5, 3]
[5, 3, 4]
[5, 4, 3]
BUILD SUCCESSFUL (total time: 0 seconds)

话说算法这种东西，似乎天生适合写成“策略接口” ———— 夫算法者，策略者也。

第一个文件： 排列和组合都要用到的阶乘类（原类名没有改，去掉了与本题无关的部分）