Random position in string array? Java

Question

Working on building a tic tac toe game. I'm trying to use as simple of methods as possible. I'm currently working on getting the cpu to randomly choose a spot in the array to place the "O" at. How do I go about doing this? This is what I have so far.

import java.util.Scanner;
import java.util.Random;
public class Player

{
    String player = "X";
    String cpu = "O";
    //private int[][] theBoard= new int [3][3] ;

    private String[][] theBoard=  {{" "," "," "}, {" "," "," "}, {" ", " "," "}};;
    Random cpuInput = new Random(); 

    private Board board1;
    public static Scanner scan = new Scanner(System.in);

public Player(Board board, String inBoard )
    {
        theBoard = theBoard;

    }

    public void computerMove()
    {
        String spacing = " ";
        for (int i = 0; i < theBoard.length; i++)
        {
            for (int j = 0; j < theBoard[i].length; j++)
            {

                //int random = cpuInput.nextInt(theBoard[i][j]);
                theBoard[2][2] = (cpu); //STUCK HERE!                
            }
        }
}

Bon · Accepted Answer · 2015-10-31 02:30:01Z

3

You need to find out the available spots on the board for computer to make a move. Then among the available spots you can randomly choose one to make a move.

In the below example, I use a list to store the available spots on the board and use Collections.shuffle() to randomize the list to achieve the purpose of making a random move.

class Spot {
    int row;
    int col;

    public Spot(int row, int col) {
        this.row = row;
        this.col = col;
    }
}

public void computerMove() {
    String spacing = " ";

    // firstly finding out the available moves for the computer
    List<Spot> availableSpots = new ArrayList<>();
    for (int i = 0; i < theBoard.length; ++i) {
        for (int j = 0; j < theBoard[i].length; ++j) {
            if (theBoard[i][j].equals(spacing)) {
                availableSpots.add(new Spot(i, j));
            }
        }
    }

    // if no available moves, do nothing, game has ended
    if (availableSpots.isEmpty()) {
        System.out.println("No more spots available on the board.");
        return;
    } else {
        // shuffle the list so that it becomes randomly orderedd
        Collections.shuffle(availableSpots);

        // get the first one of the random list
        Spot spot = availableSpots.get(0);
        theBoard[spot.row][spot.col] = (cpu);
    }
}

edited Oct 31, 2015 at 2:30

answered Oct 31, 2015 at 1:05

Bon

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2 Comments

pewpew Over a year ago

So it is saying that <Spot> is missing a 'symbol'. How would I fill this? Thanks. I have never used < > these before

Bon Over a year ago

@pewpew <> is java generics, check out this docs.oracle.com/javase/tutorial/java/generics for more information on generics; Spot is a simple class I created to wrap row and col. Have updated my code

Marcin · Accepted Answer · 2015-10-31 00:57:52Z

2

You can do it this way, generate two numbers between 0-2 and if place is not taken, place it there at index [x][y]

Random generator = new Random(); 
import java.util.*;
int x = generator.nextInt(3);
int y = generator.nextInt(3);
if place is not taken:
theBoard[x][y];
if place is taken generate again:
int x = generator.nextInt(3);
int y = generator.nextInt(3);

answered Oct 31, 2015 at 0:57

Marcin

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1 Comment

pewpew Over a year ago

Thank you for your input

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