In a tic-tac-toe game, I want to warn O player if X player will win the game if he/she choose any 1-9.
My solution is to iterate 1-9 before O player starts. If any one of 1-9 will cause X win the game, informa O player that he/she will lose game, also give him/her the exact number which will cause him/her lose the game.
My problem is that I don't know how to iterate 1-9 before //Player O's turn(in Line 87).
If you have any suggestions, that will be really helpful for me. Thank you!
My source code is as below; very appreciate for your help.
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
class TicTacToe {
public static void main(String[] args) {
new InputStreamReader(System.in);
BufferedReader theKeyboard = new BufferedReader(new InputStreamReader(System.in));
Board Game = new Board();
System.out.print("Enter 1 to play with computer;" + "\nEnter 2 to play with other people.\nPlease enter 1-2: ");
int players = 1;
String input = "";
boolean badInput = false;
do // get the number of players -- only accept 1 or 2
{
try {
input = theKeyboard.readLine();
} catch (IOException e) {
System.out.println("input error:" + e);
System.exit(1);
}
if (input.equals("1")) {
badInput = false;
players = 1;
} else if (input.equals("2")) {
badInput = false;
players = 2;
} else
badInput = true;
if (badInput)
System.out.print("Enter a number, 1 or 2: ");
} while (badInput);
System.out.println("TicTacToe Game starts." + " Please enter 1-9 to make your choice.");
int[] move = new int[2];
char winner;
int getTurn = 1; // The initialization of turns
System.out.println(Game); // print the board for first time
while (true) // loop only breaks when X or O wins, or a cat's game
{
// Player X's turn
if (getTurn % 2 != 0) {
if (players == 2) {
System.out.print("Player X, Enter 1-9 to make choice: ");
while (true) {
move = getMove();
// can't take occupied space
if (!Game.elementMarked(move[0], move[1]))
break;
System.out.println("That space is occupied.");
}
}
else // Or computer player
move = ComputerPlayer.makeMove(Game.copyBoard(), getTurn);
Game.markFirst(move[0], move[1]); // mark an X on the board
winner = Game.win(); // Check if win
if (winner != 'N')
break;
System.out.println(Game);
getTurn++; // return turn to the other player
}
// Player O's turn
System.out.print("Player O, Enter 1-9 to make choice: ");
while (true) {
move = getMove();
if (!Game.elementMarked(move[0], move[1]))
break;
System.out.println("This square has been chosen." + " Please enter a new square.");
}
Game.markSecond(move[0], move[1]);
winner = Game.win(); // Check if win
if (winner != 'N')
break;
System.out.println(Game);
getTurn++; // return turn to the other player
}
System.out.println(Game);
if (winner == 'C')
System.out.println("This is a cat's game.");
if (winner != 'C')
System.out.println("The winner is: " + winner);
}
// getMove gets the users choice and translates it into rows and columns
public static int[] getMove() {
new InputStreamReader(System.in);
BufferedReader theKeyboard = new BufferedReader(new InputStreamReader(System.in));
String input = "";
int[] move = new int[2];
boolean errorInput = false;
do {
try {
input = theKeyboard.readLine();
} catch (IOException e) {
System.out.println("input error:" + e);
System.exit(1);
}
if (input.equals("1")) {
move[0] = 0;
move[1] = 0;
errorInput = false;
} else if (input.equals("2")) {
move[0] = 0;
move[1] = 1;
errorInput = false;
} else if (input.equals("3")) {
move[0] = 0;
move[1] = 2;
errorInput = false;
} else if (input.equals("4")) {
move[0] = 1;
move[1] = 0;
errorInput = false;
} else if (input.equals("5")) {
move[0] = 1;
move[1] = 1;
errorInput = false;
} else if (input.equals("6")) {
move[0] = 1;
move[1] = 2;
errorInput = false;
} else if (input.equals("7")) {
move[0] = 2;
move[1] = 0;
errorInput = false;
} else if (input.equals("8")) {
move[0] = 2;
move[1] = 1;
errorInput = false;
} else if (input.equals("9")) {
move[0] = 2;
move[1] = 2;
errorInput = false;
} else
errorInput = true;
if (errorInput)
System.out.print("Error input. Enter a number within 1-9: ");
} while (errorInput);
return move;
}
}
/**
* ComputerPlayer is the AI client for computer, user can play with this "smart"
* computer.
*/
class ComputerPlayer {
public static int[] makeMove(int board[][], int turn) {
int square = 5;
int move[] = new int[2];
if (turn == 1) // first move is to get 5
{
square = 5;
move = Convert(square);
return move;
}
move = randomMove(board); // make a random move.
return move;
}
public static int[] randomMove(int board[][]) {
int move[] = new int[2];
int randomRow;
int randomCol;
while (true) {
randomRow = (int) (Math.random() * 3);
randomCol = (int) (Math.random() * 3);
if (board[randomRow][randomCol] == 0)
break;
}
move[0] = randomRow;
move[1] = randomCol;
return move;
}
// Convert will convert square (1-9) into a row and column
public static int[] Convert(int square) {
int move[] = new int[2];
if (square == 1) {
move[0] = 0;
move[1] = 0;
} else if (square == 2) {
move[0] = 0;
move[1] = 1;
} else if (square == 3) {
move[0] = 0;
move[1] = 2;
} else if (square == 4) {
move[0] = 1;
move[1] = 0;
} else if (square == 5) {
move[0] = 1;
move[1] = 1;
} else if (square == 6) {
move[0] = 1;
move[1] = 2;
} else if (square == 7) {
move[0] = 2;
move[1] = 0;
} else if (square == 8) {
move[0] = 2;
move[1] = 1;
} else if (square == 9) {
move[0] = 2;
move[1] = 2;
}
return move;
}
}
/**
* Board can represents 2D 3*3 array for TicTacToe game. It can check if someone
* wins or a cat's game. It can check if a square has been chosen. It can also
* mark an X or O from the player's choice.
*/
class Board {
private int[][] myBoard = new int[3][3];
// Create a 3 by 3 array and use for a tic tac toe board.
public Board() {
for (int row = 0; row < 3; row++) {
for (int column = 0; column < 3; column++) {
myBoard[row][column] = 0;
}
}
}
public int[][] copyBoard() {
return myBoard;
}
/*
* markFirst makes places a 2 accumulation for X
*/
public void markFirst(int row, int column) {
myBoard[row][column] = 2;
}
/*
* markSecond makes places a 1 accumulation for O
*/
public void markSecond(int row, int column) {
myBoard[row][column] = 1;
}
/*
* elementMarked returns a true if the space has been taken
*/
public boolean elementMarked(int row, int column) {
if (myBoard[row][column] == 0)
return false;
else
return true;
}
/*
* Win constructor checks if someone wins. Here are the meanings of each
* return type 'N' means no winner; 'X' means X won; 'O' means O won; 'C'
* means a C's game.
*/
public char win() {
char winner = 'N';
int catCheck = 1;
// Check the columns
for (int column = 0; column < 3; column++) {
int accumulation = myBoard[0][column] * myBoard[1][column] * myBoard[2][column];
if (accumulation == 8) // 2*2*2 = 8, a win for X
{
winner = 'X';
break;
}
if (accumulation == 1) // 1*1*1 = 1, a win for O
{
winner = 'O';
break;
}
}
if (winner != 'N')
return winner;
// Check the rows
for (int row = 0; row < 3; row++) {
int accumulation = myBoard[row][0] * myBoard[row][1] * myBoard[row][2];
if (accumulation == 8) {
winner = 'X';
break;
}
if (accumulation == 1) {
winner = 'O';
break;
}
}
if (winner != 'N')
return winner;
// Check one diagonal
int accumulation = myBoard[0][0] * myBoard[1][1] * myBoard[2][2];
if (accumulation == 1)
winner = 'O';
if (accumulation == 8)
winner = 'X';
// Check the other diagonal
accumulation = myBoard[0][2] * myBoard[1][1] * myBoard[2][0];
if (accumulation == 1)
winner = 'O';
if (accumulation == 8)
winner = 'X';
// If nobody's won, Check for a cat's game
if (winner == 'N') {
for (int row = 0; row < 3; row++) {
for (int column = 0; column < 3; column++) {
catCheck *= myBoard[row][column];
}
}
// any empty space is a zero. So product is zero if there is space
// left.
if (catCheck != 0)
winner = 'C';
}
return winner;
}
/*
* toString enables printing out of the board
*/
public String toString() {
String printBoard = "";
char XorO;
int position = 49; // In ASCII, 49 stands for number 1
for (int row = 0; row < 3; row++) {
for (int column = 0; column < 3; column++) {
if (myBoard[row][column] == 1)
// In ASCII, 79 stands for an O (78+1)
XorO = (char) (myBoard[row][column] + 78);
else if (myBoard[row][column] == 2)
// In ASCII, 88 stands for an X (86+2)
XorO = (char) (myBoard[row][column] + 86);
else
XorO = (char) (position);
position++;
printBoard = printBoard + XorO + " ";
}
printBoard = printBoard + "\n"; // starts a new line at the end of a
// row
}
return printBoard;
}
}
So the solution I came up with works as follows: In order to check if X(the computer) could potentially win with his next move, we first place a "theoretical/temporary"(It'll become clear later why it's temporary) 'X' in the free cells of the board. In other words, we iterate through the cells of the board one by one. If a cell is free, we place a temporary 'X' in it. We then regard the new board that we have and check if someone won. If yes, we clear the cell in which we placed the temporary 'X'(that's why it's called temporary) and return a char array of length 2 containing who won(i.e. 'X', 'O', 'C' or 'N') and the theoretical cell(1-9) that leads to that win. If no one won, we clear the cell we just filled and try the same procedure again with the next cell, and so on.
To achieve all that, I wrote a method called canWin(), which is built on your win() method with a few changes. This method returns a 2 element char array containing the who won and the position(cell index(1-9)). The method works as follows in detail: The method uses a for-loop with an index i which gets incremented from 1 to 9(the cells). First, using your convert method, we check if the cell i is occupied:
if(!elementMarked(ComputerPlayer.Convert(i)[0], ComputerPlayer.Convert(i)[1]))
If elementMarked(...) returns true, we skip this iteration in the loop and try the following cell. But if elementMarked(...) returns false, then we place an 'X' there using your markFirst(...) method:
markFirst(ComputerPlayer.Convert(i)[0], ComputerPlayer.Convert(i)[1]);
After that, using your way of checking from win(), we check if someone has won. If indeed that is the case, we save the winner and the index i in a 2 element char array called result and return result. If no one won, i gets incremented and the loop continues. This method looks like this:
public char [] canWin(){
char winner = 'N';
int catCheck = 1;
char [] result=new char[2];
for(int i=1; i<10; i++){
winner = 'N';
//Places an X if a cell is not occupied
if(!elementMarked(ComputerPlayer.Convert(i)[0], ComputerPlayer.Convert(i)[1]))
markFirst(ComputerPlayer.Convert(i)[0],ComputerPlayer.Convert(i)[1]);
else //If cell is occupied, skip this iteration
continue;
// Check the columns
for (int column = 0; column < 3; column++) {
int accumulation = myBoard[0][column] * myBoard[1][column] * myBoard[2][column];
if (accumulation == 8) // 2*2*2 = 8, a win for X
{
winner = 'X';
break;
}
if (accumulation == 1) // 1*1*1 = 1, a win for O
{
winner = 'O';
break;
}
}
if (winner != 'N'){
result[0] = winner; //register winner
result[1]=(char)i; //register cell that led to win
myBoard[ComputerPlayer.Convert(i)[0]][ComputerPlayer.Convert(i)[1]] = 0; //undoing the cell selection
return result;
}
// Check the rows
for (int row = 0; row < 3; row++) {
int accumulation = myBoard[row][0] * myBoard[row][1] * myBoard[row][2];
if (accumulation == 8) {
winner = 'X';
break;
}
if (accumulation == 1) {
winner = 'O';
break;
}
}
if (winner != 'N'){
result[0] = winner; //register winner
result[1]=(char)i; //register cell that led to win
myBoard[ComputerPlayer.Convert(i)[0]][ComputerPlayer.Convert(i)[1]] = 0; //undoing the cell selection
return result;
}
// Check one diagonal
int accumulation = myBoard[0][0] * myBoard[1][1] * myBoard[2][2];
if (accumulation == 1)
winner = 'O';
if (accumulation == 8){
winner = 'X';
result[0] = winner; //register winner
result[1]=(char)i; //register cell that led to win
myBoard[ComputerPlayer.Convert(i)[0]][ComputerPlayer.Convert(i)[1]] = 0; //undoing the cell selection
return result;
}
// Check the other diagonal
accumulation = myBoard[0][2] * myBoard[1][1] * myBoard[2][0];
if (accumulation == 1)
winner = 'O';
if (accumulation == 8){
winner = 'X';
result[0] = winner; //register winner
result[1]=(char)i; //register cell that led to win
myBoard[ComputerPlayer.Convert(i)[0]][ComputerPlayer.Convert(i)[1]] = 0; //undoing the cell selection
return result;
}
// If nobody's won, Check for a cat's game
if (winner == 'N') {
for (int row = 0; row < 3; row++) {
for (int column = 0; column < 3; column++) {
catCheck *= myBoard[row][column];
}
}
// any empty space is a zero. So product is zero if there is space
// left.
if (catCheck != 0)
winner = 'C';
}
result[0] = winner; //register winner
result[1]=(char)i; //register cell that led to win
myBoard[ComputerPlayer.Convert(i)[0]][ComputerPlayer.Convert(i)[1]] = 0; //undoing the cell selection
}
return result;
}
Now we need to implement this method in your main method. We do this by calling canWin() every time player O is about to play(i.e. after player X finishes his move). If canWin() returns 'X'(i.e. X could win with his next move), then we print out a message to the player warning him and telling him which cell he needs to occupy to prevent X winning. This looks like this:
// Player O's turn
char[] canWin=Game.canWin();
if(canWin[0]=='X') //If X could win with his next move
System.out.println("Watch out! Player X can win if he plays in cell "+(int)Game.canWin()[1]+"!");
System.out.print("Player O, Enter 1-9 to make choice: ");