SICP

Exercise 1.3. Define a procedure that takes three numbers as arguments and returns the sum of the squares of the two larger numbers.

求三个数中最大两个数字的平方和，我们可以直接比较：

(define (sum-of-square-of-largest-two-1 x y z)
  (cond ((and (> x y) (> y z))
         (+ (* x x) (* y y)))
        ((and (> x y))
         (+ (* x x) (* z z)))
        ((> x z) ; and also (< x y)
         (+ (* x x) (* y y)))
        (else
         (+ (* z z) (* y y)))))

然后对三个数进行 6 种不同顺序的测试：

(load "../testframe.scm")

(assert= (sum-of-square-of-largest-two-1 2 3 4) 25)
(assert= (sum-of-square-of-largest-two-1 2 4 3) 25)
(assert= (sum-of-square-of-largest-two-1 3 2 4) 25)
(assert= (sum-of-square-of-largest-two-1 3 4 2) 25)
(assert= (sum-of-square-of-largest-two-1 4 2 3) 25)
(assert= (sum-of-square-of-largest-two-1 4 3 2) 25)

这个过程的确满足我们的要求，但我们把所有的操作全部放到一个过程中，这使得我们如果要修改过程的某一部分就会比较困难，比如：

求 3 个数最大的两个数的三次方和
求 4 个数中最大的两个数的平方和

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