Question

I have a function ‘generateRan’ that generates random numbers. This function can not be changed.

int generateRan() {
    Random num = new Random();
    return (1 + num.nextInt(100));
}

I have to write code that will:

1. Print numbers 1-20 randomly.
2. Print numbers 1-200 randomly.

Each number should be printed only once.

The function can be used any number of times. But it is a bit heavy so I want to make the code more optimized.

Here is what I’ve coded:

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class Test {

    public static void main(String[] args) {
        List<String> list = new ArrayList();
        Test t = new Test();
        iniList(list, 20);

        for (Integer i = ((t.generateRan()) % 20); list.size() > 0; i = 1+((t
                .generateRan()) % 20)) {
            if (list.contains(i.toString())) {
                list.remove(i.toString());
                System.out.println(i);
            }
        }

        System.out.println("********");

        iniList(list, 200);


        for (Integer i = ((t.generateRan()%2)*100 + t.generateRan()) ; list.size() > 0; i = ((t.generateRan()%2)*100 + t.generateRan())) {
            if (list.contains(i.toString())) {
                list.remove(i.toString());
                System.out.println(i);
            }
        }

    }

    private static void iniList(List list, int i) {
        for (Integer k = 1; k <= i; k++) {
            list.add(k.toString());
        }
    }

    int generateRan() {
        Random num = new Random();
        return (1 + num.nextInt(100));
    }

}

Currently the code for 1-200 is incorrect.

Answer 1

Each numbers should print only once

Then all you need to to is create a List<Integer> of the entire range, then call Collections.shuffle.

private static void displayNumbers(int minInclusive, int maxInclusive) {
    List<Integer> list = new ArrayList<Integer>();
    for (int i = minInclusive; i <= maxInclusive; i++) {
        list.add(i);
    }
    Collections.shuffle(list);
    for (int value : list) {
        System.out.println(value);
    }
}

Personally I’d normally use parameters of minInclusive, maxExclusive or minInclusive, count, but it looks like it may be more readable this way for your situation.