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I'm working on building one of my fist apps and I'm building a Sudoku mobile game. I've built the random number generator I just cant figure out how to write it so that it only generates numbers between 1-9 (not zero) and each of numbers are only generated once. Here is what I have so far: 

package randomNumber;

import java.util.Random; 

public class OneToNine {

    public static final void main(String... aArgs) {
        log ("generating random integers in range 1-9");
        Random randomGenerator = new Random();
        for (int idx = 1; idx <= 9; ++idx) {
            int randomInt = randomGenerator.nextInt(9);
            log ("Generated : " + randomInt);
        }

        log("Done. ");  
    }

    private static void log (String aMessage) {
        System.out.println(aMessage);
    }

}
Joel
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Austin Farris
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3 Answers3

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Rather than worry about generating the numbers in a random order, you should adjust your approach to shuffling the numbers. You know you will have the numbers 1-9 so do something like this:

public ArrayList<Integer> getRandomOrderedNums(){ ArrayList<Integer> numbers = new ArrayList<Integer>(); for(Integer i = 1; i < 10; i++){ numbers.add(i); } Collections.shuffle(numbers); }

mistahenry
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For your second part, to see if the numbers are repeated, you can easily use a data structure such as a HashSet, which is the most efficient to check for repeated values. Let me know if you're not fully comfortable with them. Using the hashset, you can come up with a random number, and check if the set contains this number, and if it does, try again.

With regards to the random number, you can just do randomGenerator.nextInt(9) + 1 so it'll always be from 1-9 (inclusive).

StoneMan
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You might want to use a function like this:

public static int getRandInt(int max, int min) {
   return new Random().nextInt((max - min) + 1) + min;
}
Marvin
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