I need help for an exercice in school.

I need to create an array with 6 random integers from the following array : montab[] = {1,2,3,4,5,6,7,8,9,10,25,50,75,100} and with the following rules :

1. numbers 25,50,75,100 can only occur once each in the array
2. numbers 1 to 10 can only occur twice each in the array

I tried the first rule for now but in rare cases I still get the number more than once.

Here is my code :

public class Exo7bis {
public static void main (String[] args){
    Random random = new Random();
    int montab[] = {1,2,3,4,5,6,7,8,9,10,25,50,75,100};
    int[] ar1 = new int[6];
    int j = 0, compteur25 = 0, compteur50 = 0, compteur75 = 0, compteur100 = 0;
        for (int i = 0; i < ar1.length; i++) {
            ar1[i] = (montab[new Random().nextInt(montab.length)]);
            if (ar1[i] == 25) {
                compteur25++;
                if (compteur25 > 1) {
                    while (ar1[i] == 25)
                        ar1[i] = (montab[new Random().nextInt(montab.length)]);
                }
            }
            if (ar1[i] == 50) {
                compteur50++;
                if (compteur50 > 1) {
                    while (ar1[i] == 50)
                        ar1[i] = (montab[new Random().nextInt(montab.length)]);
                }
            }
            if (ar1[i] == 75) {
                compteur75++;
                if (compteur75 > 1) {
                    while (ar1[i] == 75)
                        ar1[i] = (montab[new Random().nextInt(montab.length)]);
                }
            }
            if (ar1[i] == 100) {
                compteur100++;
                if (compteur100 > 1) {
                    while (ar1[i] == 100)
                        ar1[i] = (montab[new Random().nextInt(montab.length)]);
                }
            }
        }

        for (int i = 0; i < ar1.length; i++) {
            System.out.print(ar1[i] +" ⎢ " + "\t");
        }
    }
}

I know that my tests are not totally right, I identified the problem but I can't find the proper solution.

If someone could help me or advise me, that would be cool.

Thanks in advance!

Jeremy

There are many ways to achieve this but since you are just using arrays I will advise you making a function that counts how many time 1-10 is repeated. For the first the condition you could just replace the element with 0 so it will not repeat next time. I think it's easy to explain in code so have a look at what you could change in your code:

public static void main(String[] args) {
        Random random = new Random();
        int montab[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 25, 50, 75, 100 };
        int[] ar1 = new int[6];
        int j = 0, count = 0;
        while (j < ar1.length) {
            count = 0;
            int index = random.nextInt(montab.length);
            int num = montab[index];
            if (num >= 25) { //adds any number greater or equal to 25
                ar1[j] = num;
                j++;
                montab[index] = 0; // replace the origianl array with 0.
            } else if (num != 0) {
                if(!isRepeated(ar1,num)){ //checks if the array has more than two of the number.
                ar1[j] = num;
                j++;
                }
            }
        }
        for (int i = 0; i < ar1.length; i++) {
            System.out.print(ar1[i] + " ⎢ " + "\t");
        }
    }

    public static boolean isRepeated(int[] arr, int num) { //method that verifies if the array has a number repeated twice or not.
        int count = 0;
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] == num)
                count++;
        }
        return count==2 ? true : false;
    }

I haven't tested it but I'm pretty sure it will work!!