Loading 2 random numbers into an array with no duplicates - arrays

Question

I want to generate random coordinates from 0-5 (Row,Col) without any duplicates using for loops. Basically if the numbers (3,2), (3,4), (1,4), (3,4) are generated then (3,4) will not be utilized and a new random set will be looked for.
These are the methods that generate two random numbers and loads them into the array shootP[ ]
int[] shootP = new int[2];
public static int shootRowP(int[] shootP)
{
Random rn = new Random();
shootP[0] = rn.nextInt(5)+1;//loads into ROW
System.out.print("Row:"+(shootP[0]));
return shootP[0]--;
}
public static int shootColP(int[] shootP,int[][]boardP)
{
Random rn = new Random();
shootP[1] = rn.nextInt(5)+1;//loads into Col
System.out.print(" Column:"+(shootP[1])+"/n");
return shootP[1]--;
}
I then want to have another method read in the values of shootP[0] and shootP[1] and check to see if those values were already used. Any suggestions?

Answer 1

Since the number of possible coordinates (X,Y) is not too large, first build a list of all possible coordinates. Then, at each random pick, choose a random element in this list (i.e. rn.nextInt(current_list_length)), remove the element from the list and return it.
Notes:
You must do something (exception?) when the list is empty
You can also shuffle your list at initialization and at each draw, you pick and delete the first (or last) element. See here how to shuffle an array, for example.
Instead of a list, a stack (an array + an element counter) can do the trick.