说明：  分析：用N进制的方法吧。设一个N个单元的数组，对第一个单元做加一操作，满N进 一。每加一次一就判断一下各位数组单元有无重复，有则再转回去做加一操作，没有则说明得到了一个排列方案。
(Analysis: N-band approach with it. A N-unit array, and add a unit to do one operation, over N into one. Add 1 each time you click on an array of modules to determine whether or not duplicate, then go back and have to do is add one operation, then there is no order to be a program.)