Simple AI implementation of Tic-Tac-Toe

tic_tac_toe.cpp

#include <iostream>

using namespace std;

enum players {X = 1, O = 2};

class TicTacToe{
  short state[9] = {0, 0, 0, 0, 0, 0, 0, 0, 0};

  const short strategy[9] =  { 1, 3, 1, 3, 5, 3, 1, 3, 1};
public:
	/**
	* X = 1
	* O = 2
	*/
	bool move(int player, int pos)
	{
		if(pos < 0 || pos > 8 || state[pos] != 0)
			return false;

		state[pos] = player;
	}

	short possibleWin()
	{
		//Check possible win for each player
		for (int p = 1; p < 3; ++p)
		{
			for(int i = 0; i < 9; i += 3){

				//Check for win horizontally
				if(state[0+i] == p && state[1+i] == p && state[2+i] == 0)
					return 2+i;
				else if(state[1+i] == p && state[2+i] == p && state[0+i] == 0)
					return 0+i;
				else if(state[0+i] == p && state[2+i] == p && state[1+i] == 0)
					return 1+i;

				//Check for win vertically
				if(state[0+i/3] == p && state[3+i/3] == p && state[6+i/3] == 0)
					return 6+i/3;
				else if(state[0+i/3] == p && state[6+i/3] == p && state[3+i/3] == 0)
					return 3+i/3;
				else if(state[3+i/3] == p && state[6+i/3] == p && state[0+i/3] == 0)
					return 0+i/3;
			}

			//Check for win diagonally
			if(state[0] == p && state[4] == p && state[8] == 0)
				return 8;
			else if(state[4] == p && state[8] == p && state[0] == 0)
				return 0;
			else if(state[2] == p && state[4] == p && state[6] == 0)
				return 6;
			else if(state[4] == p && state[6] == p && state[2] == 0)
				return 2;
			else if(((state[0] == p && state[8]) || (state[2] == p && state[6] == p)) && state[4] == 0)
				return 4;
		}

		//Win not possible
		return -1;
	}

	/**
	* 1 = X wins
	* 2 = O wins
	* 3 = Nobody wins
	* 0 = Game in progress
	*/
	short gameOver()
	{
		for (int p = 1; p < 3; ++p)
		{
			for(int i = 0; i < 9; i+=3){
				if(state[0+i] == p && state[1+i] == p && state[2+i] == p)
					return p;
				else if(state[0+i/3] == p && state[3+i/3] == p && state[6+i/3] == p)
					return p;
			}

			if((state[0] == p && state[4] == p && state[8] == p) || (state[2] == p && state[4] == p && state[6] == p))
				return p;
		}

		for (int i = 0; i < 9; ++i)
		{
			if(state[i] == 0)
				return 0;
		}

		return 3;
	}

	void showBoard()
	{
		for (int i = 0; i < 9; ++i)
		{
			if(state[i] == 0)
				cout<<" - ";
			else if(state[i] == 1)
				cout<<" X ";
			else if(state[i] == 2)
				cout<<" O ";

			if((i+1)%3 == 0)
				cout<<endl;
		}
		cout<<endl;
	}

	short getNextMove()
	{
		short highestPossibleMove = 0;
		short highestPossiblePos = -1;
		short possible;

		if(gameOver())
			return -1;
		else{

			if((possible = possibleWin()) != -1){
				return possible;
			}

			for (int i = 0; i < 9; ++i){
				if(state[i] == 0 && strategy[i] > highestPossibleMove){
					highestPossibleMove = strategy[i];
					highestPossiblePos = i;
				}
			}

			return highestPossiblePos;
		}
	}
	

};

int main(int argc, char** args)
{
	TicTacToe lol;

	lol.move(O, 0);
	
	while(lol.gameOver() == 0)
	{
		lol.move(X, lol.getNextMove());
		lol.showBoard();
		lol.move(O, lol.getNextMove());
		lol.showBoard();
	}

	cout<<lol.gameOver()<<endl;

	return 0;
}