Have tried debugging my MiniMax code but can't seem to find the problem here. The main method is evalGame(), which returns 1 for a win, -1 for a loss and 0 for a tie. Are there any obvious errors I have made in the MiniMax algorithm?
package tictactoe;
import static tictactoe.Player.*;
import java.util.Arrays;
public class MinimaxTTT {
private Player[] board = new Player[9];
private static Player player = X;
public MinimaxTTT() {
Arrays.fill(board, E);
player = X;
}
public MinimaxTTT(Player[] b, Player p) {
for(int i = 0; i < 9; i++) {
board[i] = b[i];
}
player = p;
}
public static boolean checkWin(Player[] b, Player p) {
if((b[0]==p&&b[1]==p&&b[2]==p)
|| (b[0]==p&&b[3]==p&&b[6]==p)
|| (b[0]==p&&b[4]==p&&b[8]==p)
|| (b[0]==p&&b[1]==p&&b[2]==p)
|| (b[1]==p&&b[4]==p&&b[7]==p)
|| (b[0]==p&&b[1]==p&&b[2]==p)
|| (b[2]==p&&b[4]==p&&b[6]==p)
|| (b[2]==p&&b[5]==p&&b[8]==p)
|| (b[0]==p&&b[3]==p&&b[6]==p)
|| (b[3]==p&&b[4]==p&&b[5]==p)
|| (b[0]==p&&b[4]==p&&b[8]==p)
|| (b[2]==p&&b[4]==p&&b[6]==p)
|| (b[3]==p&&b[4]==p&&b[5]==p)
|| (b[1]==p&&b[4]==p&&b[7]==p)
|| (b[2]==p&&b[5]==p&&b[8]==p)
|| (b[3]==p&&b[4]==p&&b[5]==p)
|| (b[0]==p&&b[3]==p&&b[6]==p)
|| (b[2]==p&&b[4]==p&&b[6]==p)
|| (b[6]==p&&b[7]==p&&b[8]==p)
|| (b[6]==p&&b[7]==p&&b[8]==p)
|| (b[1]==p&&b[4]==p&&b[7]==p)
|| (b[2]==p&&b[5]==p&&b[8]==p)
|| (b[6]==p&&b[7]==p&&b[8]==p)
|| (b[0]==p&&b[4]==p&&b[8]==p)) {
return true;
}
return false;
}
private static boolean checkTie(Player[] b) {
for(int i = 0; i < 9; i++) {
if(b[i] == E) {
return false;
}
}
return true;
}
private static boolean gameOver(Player[] b) {
return checkTie(b) || checkWin(b, X) || checkWin(b, O);
}
private static int maxOfArray(int[] a) {
int max = a[0];
for (int i : a)
if (max < i)
max = i;
return max;
}
private static int minOfArray(int[] a) {
int min = a[0];
for (int i : a)
if (min > i)
min = i;
return min;
}
private static int getEmptyNumber(Player[] b) {
int spaces = 0;
for(int i = 0; i < 9; i++) {
if(b[i] == E)
spaces++;
}
return spaces;
}
private static int evalGame(Player[] b, Player p, Player currentP) {
if(gameOver(b)) {
if(checkWin(b, p)) {
return 1;
} else if(checkWin(b, p == X ? O : X)) {
return -1;
} else {
return 0;
}
} else {
int[] arrayEval = new int[getEmptyNumber(b)];
for(int i = 0; i < getEmptyNumber(b); i++) {
arrayEval[i] = evalGame(possibleBoards(b, currentP)[i], p, currentP == X ? O : X);
}
if(currentP == p) {
return maxOfArray(arrayEval);
} else {
return minOfArray(arrayEval);
}
}
}
public static Player[][] possibleBoards(Player[] b, Player p) {
Player[][] toReturn = new Player[getEmptyNumber(b)][9];
int spaces = 0;
for(int i = 0; i < 9; i++) {
if(b[i] == E) {
for(int j = 0; j < 9; j++) {
toReturn[spaces][j] = b[j];
}
toReturn[spaces][i] = p;
spaces++;
}
}
return toReturn;
}
public static void main(String[] args) {
Player[] p = new Player[9];
Arrays.fill(p, E);
p[1] = X;
System.out.println(evalGame(p, O, O));
}
}
I have since looked over my code and realised I made a mistake while debugging. The working, edited code is below for anyone who is interested
package tictactoe;
import static tictactoe.Player.*;
import java.util.Arrays;
public class MinimaxTTT {
private Player[] board = new Player[9];
private Player player = X;
public MinimaxTTT() {
Arrays.fill(board, E);
player = X;
}
public MinimaxTTT(Player[] b, Player p) {
for(int i = 0; i < 9; i++) {
board[i] = b[i];
}
player = p;
}
public Player[] getBoard() {
return board;
}
public void setBoard(Player[] b) {
for(int i = 0; i < 9; i++) {
board[i] = b[i];
}
}
public void setSquare(int i, Player p) {
board[i] = p;
}
public Player getPlayer() {
return player;
}
public void setPlayer(Player p) {
player = p;
}
public void switchPlayers() {
player = player == X ? O : X;
}
public boolean checkWin(Player[] b, Player p) {
if(b[0] == p && b[1] == p && b[2] == p
|| b[3] == p && b[4] == p && b[5] == p
|| b[6] == p && b[7] == p && b[8] == p
|| b[0] == p && b[3] == p && b[6] == p
|| b[1] == p && b[4] == p && b[7] == p
|| b[2] == p && b[5] == p && b[8] == p
|| b[0] == p && b[4] == p && b[8] == p
|| b[2] == p && b[4] == p && b[6] == p) {
return true;
}
return false;
}
public boolean checkTie(Player[] b) {
for(int i = 0; i < 9; i++) {
if(b[i] == E) {
return false;
}
}
return true;
}
public boolean gameOver(Player[] b) {
return checkTie(b) || checkWin(b, X) || checkWin(b, O);
}
private int maxOfArray(int[] a) {
int max = a[0];
for (int i : a)
if (max < i)
max = i;
return max;
}
private int minOfArray(int[] a) {
int min = a[0];
for (int i : a)
if (min > i)
min = i;
return min;
}
private int getEmptyNumber(Player[] b) {
int spaces = 0;
for(int i = 0; i < 9; i++) {
if(b[i] == E)
spaces++;
}
return spaces;
}
private int findIndex(int[] is, int n) {
for(int i = 0; i < is.length; i++) {
if(is[i] == n)
return i;
}
return 0;
}
private int[] evalGame(Player[] b, Player p, Player currentP, int depth) {
int[] toReturn = new int[2];
if(gameOver(b)) {
if(checkWin(b, p)) {
toReturn[1] = 10 + depth;
return toReturn;
} else if(checkWin(b, p == X ? O : X)) {
toReturn[1] = depth - 10;
return toReturn;
} else {
toReturn[1] = 0;
return toReturn;
}
} else {
depth += 1;
int[] arrayEval = new int[getEmptyNumber(b)];
for(int i = 0; i < getEmptyNumber(b); i++) {
arrayEval[i] = evalGame(possibleBoards(b, currentP)[i], p, currentP == X ? O : X, depth)[1];
}
if(currentP == p) {
int position = findIndex(arrayEval, maxOfArray(arrayEval));
int base = 0;
for(int i = 0; i < 9; i++) {
if(b[i] == E) {
if(base == position) {
toReturn[0] = i;
break;
} else {
base++;
}
}
}
toReturn[1] = maxOfArray(arrayEval);
return toReturn;
} else {
toReturn[1] = minOfArray(arrayEval);
return toReturn;
}
}
}
public Player[][] possibleBoards(Player[] b, Player p) {
Player[][] toReturn = new Player[getEmptyNumber(b)][9];
int spaces = 0;
for(int i = 0; i < 9; i++) {
if(b[i] == E) {
for(int j = 0; j < 9; j++) {
toReturn[spaces][j] = b[j];
}
toReturn[spaces][i] = p;
spaces++;
}
}
return toReturn;
}
public Player[] move() {
if(!gameOver(board)) {
board[evalGame(board, player, player, 0)[0]] = player;
}
return board;
}
}