How to generate 6 different random numbers in java

Question

I want to generate 6 different random numbers by using Math.random and store them into an array. How can I make sure that they are different? I know I need to use for-loop t

Answer 1

Generate any 6 numbers (not necessarily different). Order them.

a1 <= a2 <= a3 <= a4 <= a5 <= a6

Now take these 6 numbers

a1 < a2 + 1 < a3 + 2 < a4 + 3 < a5 + 4 < a6 + 5

These 6 are different and random.

The idea of this construct comes from some combinatorial proofs.

Its advantage is that it's simple, fast, and deterministic.
I think the time complexity is O(count*log(count)).
I wonder if it can be improved.

import java.util.TreeMap;

public class Test005 {

    public static void main(String[] args) {
        int count = 6;
        int min = 1;
        int max = 49;

        // random number mapped to the count of its occurrences
        TreeMap mp = new TreeMap();
        for (int i=0; i