為了熟悉 clojure，刷題練習語法

Get the mean of an array

回傳最接近陣列平均數的整數(無條件捨去)，且不會給空陣列
Return the average of the given array rounded down to its nearest integer.
The array will never be empty.

下列為題目的測試：

(ns marks-test
  (:require [clojure.test :refer :all]
            [marks :refer :all]))

(deftest simple-test
  (is (= (get-average [2, 2, 2, 2]) 2))
  (is (= (get-average [1, 5, 87, 45, 8, 8]) 25))
  (is (= (get-average [2,5,13,20,16,16,10]) 11))
  (is (= (get-average [1,2,15,15,17,11,12,17,17,14,13,15,6,11,8,7]) 11)))

Solution 1:

;; (Math/floor m) will return a float & int will coerce to integer

(ns marks)


(defn get-average [marks]
  (int (Math/floor (/ (reduce + marks) (count marks))))
  )

個別使用後發現其實不需要 Math/floor 就可以達到取整數的目的：

• int 取整數
• Math/floor 無條件捨去，可以用於整數
• Math/ceil 無條件進位，可以用於整數
• Math/round 四捨五入，不能用於整數

(int 1.3)              ;; 1
(int 1.5)              ;; 1
(int 1)                ;; 1

(Math/floor 1.3)       ;; 1.0
(Math/floor 1.5)       ;; 1.0
(Math/floor 1)         ;; 1.0

(int (Math/floor 1.3)) ;; 1
(int (Math/floor 1.5)) ;; 1
(int (Math/floor 1))   ;; 1

(Math/ceil 1.3)        ;; 2.0
(Math/ceil 1.5)        ;; 2.0
(Math/ceil 1)          ;; 1.0

(int (Math/ceil 1.3))  ;; 2
(int (Math/ceil 1.5))  ;; 2
(int (Math/ceil 1))    ;; 1

(Math/round 1.3)  ;; 1
(Math/round 1.5)  ;; 2
(Math/round 1.0)  ;; 1
(Math/round 1)    ;; IllegalArgumentException No matching method found: round  clojure.lang.Reflector.invokeMatchingMethod (Reflector.java:80)

Solution 2:

;; In this case, int can be used when rounded down to nearest integer
(ns marks)

(defn get-average [marks]
  (int (/ (reduce + marks) (count marks))))

Solution 3:

;; (quot m n) is the value of m/n, rounded towards 0 to the nearest integer.
;; m, n need not be integers.

(ns marks)

(defn get-average [marks]
  (quot (apply + marks) (count marks)))