判断由参数中的四个点是否构成一个正方形。

Square.scala

 package com.example

 import scala.math._
 object Square extends App {
   case class Point(x: Int, y: Int)
   implicit class CombinatorialList[A](l: List[A]) {
     val xsize = l.size
     def xcombinations(n: Int): List[List[A]] =
       if (n > xsize) Nil
       else l match {
         case _ :: _ if n == 1 => l.map(List(_))
         case hd :: tl => tl.xcombinations(n - 1).map(hd :: _) ::: tl.xcombinations(n)
         case _ => Nil
       }
   }
   def isSquare(p1: Point, p2: Point, p3: Point, p4: Point): Boolean = {
     def apow(a: Int, b: Int) = pow(a - b, 2)
     def distance(a: Point, b: Point) = sqrt(apow(a.x, b.x) + apow(a.y, b.y))

     List(p1, p2, p3, p4).xcombinations(2).map(t => distance(t(0), t(1))).distinct.size == 2
   }

   assert(!isSquare(Point(1, 6), Point(6, 7), Point(2, 7), Point(9, 1)))
   assert(!isSquare(Point(4, 1), Point(3, 4), Point(0, 5), Point(1, 2)))
   assert(isSquare(Point(4, 6), Point(5, 5), Point(5, 6), Point(4, 5)))
 }