for (int i = 0; < arr.length;i++) {
			int guess = random.nextInt(arr.length);
			for (int x = 0; x < i; x++) {
				if(guess == arr[x]){
					guess = random.nextInt(arr.length);

				}
			}
				arr[i] = guess;
		}

for(int i = 0;i < arr.length;i++){ // iterate    O(N)
			int guess;
			while(check[guess = random.nextInt(arr.length)]){
				++counter;
			};
			check[guess] = true;
			arr[i] = guess;
		}