NonRepeatingChoices.java

import java.util.Random;
import java.util.stream.IntStream;
import java.util.stream.Stream;
import java.util.Collections;
import java.util.stream.Collectors;
import java.util.List;
import java.util.ArrayList;

public class NonRepeatingChoices{
    
    static Random ng;
    static int min = 1;
    static int max = 49;
    static int choices = 40;
    
    
	static public int[] chooseAndCheck(){
		int[] out = new int[choices];
		
		for(int i = 0; i<choices; i++){
		    boolean selected = false;
		    while(!selected){
		        selected = true;
		        int next = ng.nextInt(max - min + 1) + min;
		        for(int k = 0; k<=i; k++){
		            if(out[k]==next){
		                selected=false;
		                break;
		            }
		        }
		        if(selected){
		        	out[i] = next;
		        }
		    }
		}
		return out;
		
	}
	
	static public int[] shuffleAndSelect(){
		
		List<Integer> ints = IntStream.rangeClosed(min, max).boxed().collect(Collectors.toList());
		Collections.shuffle(ints, ng);
		int[] out = new int[choices];
		for(int i = 0; i<choices; i++){
		    out[i] = ints.get(i);
		}
		return out;
	}
	
	static public int[] chooseAndRemove(){
		int[] out = new int[choices];
		List<Integer> ints = IntStream.rangeClosed(min, max).boxed().collect(Collectors.toList());
		for(int i = 0; i<choices; i++){
			int dex = ng.nextInt(ints.size());
			int choice = ints.get(dex);
			ints.remove(dex);
		    out[i] = choice;
		}
		return out;
	}
	
	public static void main(String[] args){
		long start;
		int steps = 1000000;
		int sum;
		
		for(int j = 1; j<100; j++){
		
			start = System.currentTimeMillis();
			ng = new Random(j);
			sum = 0;
			for(int i = 0; i<steps; i++){
				sum += chooseAndCheck()[0];
			}
			System.out.println(System.currentTimeMillis() - start + "ms repeat " + sum);
		
		
			start = System.currentTimeMillis();
			ng = new Random(j);
			sum = 0;
			for(int i = 0; i<steps; i++){
				sum += shuffleAndSelect()[0];
			}
		
			System.out.println(System.currentTimeMillis() - start + "ms shuffle" + sum);
			
						start = System.currentTimeMillis();
			ng = new Random(j);
			sum = 0;
			for(int i = 0; i<steps; i++){
				sum += chooseAndRemove()[0];
			}
		
			System.out.println(System.currentTimeMillis() - start + "ms remove" + sum);

		}
	}

}