java实现的表达式计算器

A Convex Hull is the smallest convex polygon that contains every point of the set S. A polygon P is convex if and only if, for any two points A and B inside the polygon, the line segment AB is inside P. One way to visualize a convex hull is to put

排列组合的源代码， java实现能实现C(M,N)和P(M,N)的任意对象排列组合-combine and permute algrithm, implemented by java.