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tictactoe.cpp
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tictactoe.cpp
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#include <iostream>
#include <vector>
#include <cstdlib>
#include <ctime>
#include <utility>
using namespace std;
const char PLAYER = 'X';
const char COMPUTER = 'O';
const char EMPTY = ' ';
void printBoard(const vector<vector<char> >& board) {
for (int i = 0; i < 3; ++i) {
for (int j = 0; j < 3; ++j) {
cout << board[i][j];
if (j < 2) cout << " | ";
}
cout << endl;
if (i < 2) cout << "--|---|--" << endl;
}
}
bool isMovesLeft(const vector<vector<char> >& board) {
for (int i = 0; i < 3; ++i)
for (int j = 0; j < 3; ++j)
if (board[i][j] == EMPTY)
return true;
return false;
}
int evaluate(const vector<vector<char> >& b) {
// Checking for Rows for X or O victory.
for (int row = 0; row < 3; row++) {
if (b[row][0] == b[row][1] && b[row][1] == b[row][2]) {
if (b[row][0] == PLAYER)
return +10;
else if (b[row][0] == COMPUTER)
return -10;
}
}
// Checking for Columns for X or O victory.
for (int col = 0; col < 3; col++) {
if (b[0][col] == b[1][col] && b[1][col] == b[2][col]) {
if (b[0][col] == PLAYER)
return +10;
else if (b[0][col] == COMPUTER)
return -10;
}
}
// Checking for Diagonals for X or O victory.
if (b[0][0] == b[1][1] && b[1][1] == b[2][2]) {
if (b[0][0] == PLAYER)
return +10;
else if (b[0][0] == COMPUTER)
return -10;
}
if (b[0][2] == b[1][1] && b[1][1] == b[2][0]) {
if (b[0][2] == PLAYER)
return +10;
else if (b[0][2] == COMPUTER)
return -10;
}
// Else if none of them have won then return 0
return 0;
}
int minimax(vector<vector<char> >& board, int depth, bool isMax) {
int score = evaluate(board);
// If Maximizer has won the game return evaluated score
if (score == 10)
return score - depth;
// If Minimizer has won the game return evaluated score
if (score == -10)
return score + depth;
// If there are no more moves and no winner then it is a tie
if (!isMovesLeft(board))
return 0;
// If this maximizer's move
if (isMax) {
int best = -1000;
// Traverse all cells
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
// Check if cell is empty
if (board[i][j] == EMPTY) {
// Make the move
board[i][j] = PLAYER;
// Call minimax recursively and choose the maximum value
best = max(best, minimax(board, depth + 1, !isMax));
// Undo the move
board[i][j] = EMPTY;
}
}
}
return best;
}
// If this minimizer's move
else {
int best = 1000;
// Traverse all cells
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
// Check if cell is empty
if (board[i][j] == EMPTY) {
// Make the move
board[i][j] = COMPUTER;
// Call minimax recursively and choose the minimum value
best = min(best, minimax(board, depth + 1, !isMax));
// Undo the move
board[i][j] = EMPTY;
}
}
}
return best;
}
}
pair<int, int> findBestMove(vector<vector<char> >& board) {
int bestVal = 1000;
pair<int, int> bestMove = make_pair(-1, -1);
// Traverse all cells, evaluate minimax function for all empty cells. Return the cell with optimal value.
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
if (board[i][j] == EMPTY) {
board[i][j] = COMPUTER;
int moveVal = minimax(board, 0, true);
board[i][j] = EMPTY;
if (moveVal < bestVal) {
bestMove = make_pair(i, j);
bestVal = moveVal;
}
}
}
}
return bestMove;
}
int main() {
vector<vector<char> > board(3, vector<char>(3, EMPTY));
int row, col;
printBoard(board);
while (true) {
cout << "Player's turn (enter row and column): ";
cin >> row >> col;
if (board[row][col] != EMPTY) {
cout << "Invalid move! Try again." << endl;
continue;
}
board[row][col] = PLAYER;
if (evaluate(board) == 10) {
printBoard(board);
cout << "Player wins!" << endl; // will never happen
break;
}
if (!isMovesLeft(board)) {
printBoard(board);
cout << "It's a tie!" << endl;
break;
}
pair<int, int> bestMove = findBestMove(board);
board[bestMove.first][bestMove.second] = COMPUTER;
if (evaluate(board) == -10) {
printBoard(board);
cout << "Computer wins!" << endl;
break;
}
if (!isMovesLeft(board)) {
printBoard(board);
cout << "It's a tie!" << endl;
break;
}
printBoard(board);
}
return 0;
}