Question

写一个while循环，选择并显示一个随机的两个数字组（1-99），当它们加在一起时可以被7整除。继续直到用户说他们已经“完成”。

我不知道如何使这两个随机数与7平分我试过if语句，但它仍然不起作用。

这是我到目前为止所得到的：

public static void main(String []args)
{
    Scanner scan= new Scanner (System.in);
    String answer="Yes";

    System.out.println("Run the program?");
    answer= scan.nextLine();


    while(!answer.equalsIgnoreCase("done") )
    {
        int a=1;
        int b=1;
        a=(int) (Math.random()*99) + 1;
        b=(int) (Math.random()*99) + 1;
        if ((a + b) % 7 == 0) 
        {
            System.out.println(a + " + " + b + "= " +(a+b));
        }

        System.out.println("Do you want to continue?");
        answer= scan.nextLine();
    }

Answer 1

首先，我更喜欢Random.nextInt(int)，因为它更容易阅读（和使用）。然后，您可以使用b modulo a + b的结果调整7（因为这是余数）。像，

Random rand = new Random();
while (!answer.equalsIgnoreCase("done")) {
    int a = 1 + rand.nextInt(99);
    int b = 1 + rand.nextInt(99);
    // Updated based on @JimGarrison's comment.
    if (b < 7) {
        b = 7 - a;
    } else if (b > 93) {
        b = 98 - a;
    } else {
        b -= (a + b) % 7;
    }
    System.out.println(a + " + " + b + " = " + (a + b));
    System.out.println("Do you want to continue?");
    answer = scan.nextLine();
}

Answer 2

由于它是随机的，所以得到（a + b）％7！= 0的情况可能会占用很多。

所以我认为这效率不高：

        Scanner scan = new Scanner(System.in);
        String answer = "Yes";

        System.out.println("Run the program?");
        answer = scan.nextLine();
        int LIMIT = 99;
        List<Integer> divisible7List = new ArrayList<Integer>();

        // Generate elements that divisible by 7 that less than 99 + 99
        int count = 1;
        int divisible7 = 7 * count;
        int maxDivisible7 = LIMIT + LIMIT;
        while (divisible7 < maxDivisible7) {
            divisible7List.add(divisible7);
            divisible7 = 7 * (++count);
        }

        int size = divisible7List.size();
        StringBuilder sb = new StringBuilder();
        Random rand = new Random();
        while (!answer.equalsIgnoreCase("done")) {
            int idx = rand.nextInt(size - 1);
            int sumab = divisible7List.get(idx);
            int a = 1 + rand.nextInt(sumab);
            int b = sumab - a;

            sb.append(a);
            sb.append(" + ");
            sb.append(b);
            sb.append(" = ");
            sb.append(sumab);
            System.out.println(sb.toString());
            sb.setLength(0);
            System.out.println("Do you want to continue?");
            answer = scan.nextLine();
        }

为了等待+ b适合您的需要，只需预先生成需要并找到a和b。

虽然Loop建议？

2 个答案: