Random Combination From an Array (Java)

Question

I am creating a simple Mastermind game, where my colors are represented by numbers from 0 to 9. The program should generate a random code with length from 3 to 9 digits. I decided to use an array to hold my numbers 0 to 9, but I don't know how to generate a random number with a random length from this array. Can somebody help me please ?

Answer 1

Use the random number generator:

Random rnd=new Random()
int x=rnd.nextInt(10)

Answer 2

Here is the sample code:

package testing.Tests_SO;

import java.util.Arrays;
import java.util.Random;

public class App14487237 {

    // creating random number generator object
    public static final Random rnd = new Random();

    public static int[] getNumber() {

        // generating array length as rundom from 3 to 9 inclusive
        int length = rnd.nextInt(7) + 3;

        // creating an array
        int[] number = new int[length];

        // filling an array with random numbers from 0 to 9 inclusive
        for(int i=0; i<number.length; ++i) {
            number[i] = rnd.nextInt(10);
        }

        // returning and array
        return number;

    }


    public static void main(String[] args) {

        // generating number 10 times and prin result
        for(int i=0; i<10; ++i) {
            System.out.println( "attempt #" + i + ": " + Arrays.toString( getNumber()  ) );
        }
    }
}

Here is it's output:

attempt #0: [0, 2, 6, 2, 5, 7, 5, 3]
attempt #1: [6, 2, 6, 6, 6, 2]
attempt #2: [8, 9, 6]
attempt #3: [6, 4, 7, 2, 1, 5, 7, 0]
attempt #4: [8, 2, 6, 7, 3, 8, 2, 9, 1]
attempt #5: [8, 6, 5, 9, 8, 8, 3, 9]
attempt #6: [6, 2, 3, 8, 6]
attempt #7: [3, 4, 6, 2]
attempt #8: [0, 5, 0, 0, 5, 8, 9, 4, 6]
attempt #9: [2, 2, 3, 3, 4, 9, 0]

P.S.

To print close:

int[] number;
for(int i=0; i<10; ++i) {
    number = getNumber();
    System.out.print( "attempt #" + i + ": " );
    for(int j=0; j<number.length; ++j ) {
        System.out.print(number[j]);
    }
    System.out.println();
}

Answer 3

Use a random number generator to determine the length of the string.

Then use a random number generator in a for loop to choose each digit from your array.

Something like this:

// the array of valid numbers
int[] numbers = // intialize this however you want

Random rand = new Random();

// determine random length between 3 and 9
int numLength = rand.nextInt(7) + 3;

StringBuilder output = new StringBuilder();

for (int i = 0; i < numLength; i++) {
    // use a random index to choose a number from array
    int thisNum = rand.nextInt(numbers.length);
    // append random number from array to output 
    output.append(thisNum);
}

System.out.println(output.toString());

Answer 4

I believe what you want is part of a random permutation of the elements in your array. This could be done in two steps.

1. Use a random generator to repeatedly swap elements in the array.

   int n = arr.length;
   for (int i = 0; i < n-1; i++) {
       int j = i + rnd.nextInt(n-i); // select element between i and n
       // swap elements i and j in the array
   }
   

2. Select a random length ln and take the elements from 0 to ln