带AI功能的3x3画井字游戏（指针版本）

// Tic-Tac-Toe 2.0
// Plays the game of tic-tac-toe against a human opponent
// Uses pointers instead of refernces for function parameters


#include <iostream>
#include <string>
#include <vector>
#include <algorithm>


using namespace std;


// global constants
const char X = 'X';
const char O = 'O';
const char EMPTY = ' ';
const char TIE = 'T';
const char NO_ONE = 'N';


// function prototypes
void instructions();
char askYesNo(string question);
int askNumber(string question, int high, int low = 0);
char humanPiece();
char opponent(char piece);
void displayBoard(const vector<char>* const pBoard);
char winner(const vector<char>* const pBoard);
bool isLegal(const vector<char>* const pBoard, int move);
int humanMove(const vector<char>* const pBoard, char human);
int computerMove(vector<char> board, char computer);
void announceWinner(char winner, char computer, char human);


// main function
int main()
{
int move;
const int NUM_SQUARES = 9;
vector<char> board(NUM_SQUARES, EMPTY);


instructions();
char human = humanPiece();
char computer = opponent(human);
char turn = X;
displayBoard(&board);


while (winner(&board) == NO_ONE)
{
if (turn == human)
{
move = humanMove(&board, human);
board[move] = human;
}
else
{
move = computerMove(board, computer);
board[move] = computer;
}
displayBoard(&board);
turn = opponent(turn);
}


announceWinner(winner(&board), computer, human);


return 0;
}


// functions
void instructions()
{
cout << "Welcome to the ultimate man-machine showdown: Tic-Tac-Toe.\n";
cout << "--where human brain is pit against silicon processor\n\n";


cout << "Make your move known by entering a number, 0 - 8.  The number\n";
cout << "corresponds to the desired board position, as illustrated:\n\n";


cout << "       0 | 1 | 2\n";
cout << "       ---------\n";
cout << "       3 | 4 | 5\n";
cout << "       ---------\n";
cout << "       6 | 7 | 8\n\n";


cout << "Prepare yourself, human.  The battle is about to begin.\n\n";
}


char askYesNo(string question)
{
char response;
do
{
cout << question << " (y/n): ";
cin >> response;
} while (response != 'y' && response != 'n');


return response;
}


int askNumber(string question, int high, int low)
{
int number;
do
{
cout << question << " (" << low << " - " << high << "): ";
cin >> number;
} while (number > high || number < low);


return number;
}


char humanPiece()
{
char go_first = askYesNo("Do you require the first move?");
if (go_first == 'y')
{
cout << "\nThen take the first move.  You will need it.\n";
return X;
}
else
{
cout << "\nYour bravery will be your undoing... I will go first.\n";
return O;
}
}


char opponent(char piece)
{
if (piece == X)
{
return O;
}
else
{
return X;
}
}


void displayBoard(const vector<char>* const pBoard)
{
cout << "\n\t" << (*pBoard)[0] << " | " << (*pBoard)[1] << " | " << (*pBoard)[2];
cout << "\n\t" << "---------";
cout << "\n\t" << (*pBoard)[3] << " | " << (*pBoard)[4] << " | " << (*pBoard)[5];
cout << "\n\t" << "---------";
cout << "\n\t" << (*pBoard)[6] << " | " << (*pBoard)[7] << " | " << (*pBoard)[8];
cout << "\n\n";
}


char winner(const vector<char>* const pBoard)
{
// all possible winning rows
const int WINNING_ROWS[8][3] = { {0, 1, 2},
{3, 4, 5},
{6, 7, 8},
{0, 3, 6},
{1, 4, 7},
{2, 5, 8},
{0, 4, 8},
{2, 4, 6} };
const int TOTAL_ROWS = 8;


// if any winning row has three values that are the same (and not EMPTY),
// then we have a winner
for(int row = 0; row < TOTAL_ROWS; ++row)
{
if ( ((*pBoard)[WINNING_ROWS[row][0]] != EMPTY) &&
((*pBoard)[WINNING_ROWS[row][0]] == (*pBoard)[WINNING_ROWS[row][1]]) &&
((*pBoard)[WINNING_ROWS[row][1]] == (*pBoard)[WINNING_ROWS[row][2]]) )
{
return (*pBoard)[WINNING_ROWS[row][0]];
}
}


// since nobody has won, check for a tie (no empty squares left)
if (count(pBoard->begin(), pBoard->end(), EMPTY) == 0)
return TIE;


// since nobody has won and it isn't a tie, the game ain't over
return NO_ONE;
}


inline bool isLegal(int move, const vector<char>* pBoard)
{
return ((*pBoard)[move] == EMPTY);
}


int humanMove(const vector<char>* const pBoard, char human)
{
int move = askNumber("Where will you move?", (pBoard->size() - 1));
while (!isLegal(move, pBoard))
{
cout << "\nThat square is already occupied, foolish human.\n";
move = askNumber("Where will you move?", (pBoard->size() - 1));
}
cout << "Fine...\n";
return move;
}


int computerMove(vector<char> board, char computer)
{ 
unsigned int move = 0;
bool found = false;


//if computer can win on next move, that抯 the move to make
while (!found && move < board.size())
{
if (isLegal(move, &board))
{
//try move
board[move] = computer;
//test for winner
found = winner(&board) == computer;   
//undo move
board[move] = EMPTY;
}


if (!found)
{
++move;
}
}


//otherwise, if opponent can win on next move, that's the move to make
if (!found)
{
move = 0;
char human = opponent(computer);


while (!found && move < board.size())
{
if (isLegal(move, &board))
{
//try move
board[move] = human;  
//test for winner
found = winner(&board) == human;     
//undo move
board[move] = EMPTY;        
}


if (!found)
{
++move;
}
}
}


//otherwise, moving to the best open square is the move to make
if (!found)
{
move = 0;
unsigned int i = 0;


const int BEST_MOVES[] = {4, 0, 2, 6, 8, 1, 3, 5, 7};
//pick best open square
while (!found && i <  board.size())
{
move = BEST_MOVES[i];
if (isLegal(move, &board))
{
found = true;
}


++i;
}
}


cout << "I shall take square number " << move << endl;
return move;
}


void announceWinner(char winner, char computer, char human)
{
if (winner == computer)
{
cout << winner << "'s won!\n";
cout << "As I predicted, human, I am triumphant once more -- proof\n";
cout << "that computers are superior to humans in all regards.\n";
}


else if (winner == human)
{
cout << winner << "'s won!\n";
cout << "No, no!  It cannot be!  Somehow you tricked me, human.\n";
cout << "But never again!  I, the computer, so swear it!\n";
}


else
{
cout << "It's a tie.\n";
cout << "You were most lucky, human, and somehow managed to tie me.\n";
cout << "Celebrate... for this is the best you will ever achieve.\n";
}
}