SICP 实例 ExchangeMoney

(define (first-denomination kinds-of-coin)
(cond ((= kinds-of-coin 1) 1)
((= kinds-of-coin 2) 5)
((= kinds-of-coin 3) 10)
((= kinds-of-coin 4) 25)
((= kinds-of-coin 5) 50)))

(define (cc amount kinds-of-coin)
(cond ((= amount 0) 1)
((or (< amount 0) (= kinds-of-coin 0)) 0)
(else (+ (cc amount
(- kinds-of-coin 1))
(cc (- amount
(first-denomination kinds-of-coin))
kinds-of-coin)))))

(define (count-change amount)
(cc amount 5))

(count-change 100)

 

 

 

Java实现:

/**
 * Created by Ramble on 2017/11/22.
 */
public class ExchangeMoney {

    public static int first_denomination(int kinds_of_coin) {
        switch (kinds_of_coin) {
            case 1: {
                return 1;
            }
            case 2: {
                return 5;

            }
            case 3: {
                return 10;

            }
            case 4: {
                return 25;

            }
            case 5: {
                return 50;

            }
            default:
                return 0;
        }

    }

    public static int cc(int amount, int kinds_of_coin) {
        if (amount==0) {
            return 1;
        } else if (amount<0||kinds_of_coin==0) {
            return 0;
        } else {
            return cc(amount, kinds_of_coin-1) + cc(amount - first_denomination(kinds_of_coin), kinds_of_coin);
        }
    }

    public static int count_change(int amount) {
        return cc(amount, 5);
    }

    public static void main(String[] args) {
        long startTime = System.currentTimeMillis();
        System.out.println(count_change(1000));
        long endTime = System.currentTimeMillis();
        System.out.println("程序运行时间："+(endTime-startTime)+"ms");
    }
}