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/***
This file is part of Let's play gomoku!
Copyright (C) 2021 Aleksandr D. Goncharov (Joursoir) <chat@joursoir.net>
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.
***/
#include <stdlib.h>
#include <time.h>
#include "ai.hpp"
#include "GameField.hpp"
enum scores {
MIN_SCORE = -1000,
MAX_SCORE = 1000,
NONE_SCORE = 0,
DRAW_SCORE = 2,
WIN_SCORE = 10,
LOSE_SCORE = -10
};
AI::AI(int p, int d) : player(p), max_depth(d), first_move(true)
{
srand(time(NULL));
}
void AI::GetBestMove(int &my, int &mx, GameField field)
{
int score = MIN_SCORE;
int rows = field.GetRows();
int cols = field.GetCols();
// give chance to user :)
if(first_move) {
do {
my = rand() % rows;
mx = rand() % cols;
} while( !field.CanMove(my, mx) );
first_move = false;
return;
}
int y, x;
for(y = 0; y < rows; y++) {
for(x = 0; x < cols; x++)
{
if(!field.CanMove(y, x))
continue;
field.Move(y, x);
int result = MinMax(field, score, MAX_SCORE, 1);
field.UndoMove(y, x);
if(result > score) {
score = result;
my = y;
mx = x;
}
}
}
}
int AI::score(GameField field)
{
int state = field.GetState();
if(state == G_DRAW)
return DRAW_SCORE;
if(state == G_XPLAYER)
return player == G_XPLAYER ? WIN_SCORE : LOSE_SCORE;
if(state == G_OPLAYER)
return player == G_OPLAYER ? WIN_SCORE : LOSE_SCORE;
return NONE_SCORE;
}
// MIN_SCORE, MAX_SCORE
int AI::MinMax(GameField field, int alpha, int beta, int depth)
{
if(field.GetState() != G_NONE || depth >= max_depth) {
return score(field);
}
int score = beta;
int rows = field.GetRows();
int cols = field.GetCols();
int y, x;
for(y = 0; y < rows; y++) {
for(x = 0; x < cols; x++)
{
if(!field.CanMove(y, x))
continue;
field.Move(y, x);
int result = MinMax(field, alpha, score, depth + 1);
field.UndoMove(y, x);
if(result < score)
score = result;
if(alpha >= score)
return score;
}
}
return score;
}
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