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MinimaxAlgo.cs
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MinimaxAlgo.cs
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using System;
using System.Linq;
using System.Collections.Generic;
using System.Threading.Tasks;
namespace TicTacToe
{
public enum Difficulty
{
Easy,
Medium,
Hard
}
public class MinimaxAlgo
{
private class Moves
{
public (int score, int depth) BestResult = (Int32.MinValue, Int32.MaxValue);
public Dictionary<(int x, int y), (int score, int depth)> BestMoves;
public List<(int x, int y)> WorseMoves;
}
private static Random Random = new Random();
private static Kind AI_type;
private static Moves GetMoves(Board _currentBoard, int depth)
{
//int bestScore = int.MinValue;
//int minDepth = int.MaxValue;
var bestResult = (score: Int32.MinValue, depth: Int32.MaxValue);
var best_moves = new Dictionary<(int x, int y), (int score, int depth)>();
var worse_moves = new List<(int x, int y)>();
AI_type = _currentBoard.CurrentPlayer.Type;
int max_x = _currentBoard.GetState().GetLength(1), max_y = _currentBoard.GetState().GetLength(0);
for (int y = 0; y < max_y; y++)
{
for (int x = 0; x < max_x; x++)
{
if (_currentBoard.SetMove(x, y))
{
var result = MinMax(_currentBoard.Clone(), AI_type == _currentBoard.CurrentPlayer.Type, int.MinValue, int.MaxValue, depth);
_currentBoard.UndoLastMove();
if ((result.score >= bestResult.score)
|| (result.score == bestResult.score && result.depth < bestResult.depth))
{
best_moves.Add((x, y), result);
bestResult = result;
}
else
worse_moves.Add((x, y));
}
}
}
return new Moves{ BestMoves = best_moves, WorseMoves = worse_moves, BestResult = bestResult };
}
public static (int x, int y) BestMove(Board _currentBoard, int depth)
{
var moves = GetMoves(_currentBoard, depth);
var move = (-1, -1);
var best_moves = moves.BestMoves.Keys.ToList();
foreach(var mv in moves.BestMoves)
{
if (mv.Value.score != moves.BestResult.score
|| (mv.Value.score == moves.BestResult.score && mv.Value.depth > moves.BestResult.depth))
best_moves.Remove(mv.Key);
}
if (best_moves.Count > 0)
move = best_moves[Random.Next(best_moves.Count)];
else if (moves.WorseMoves.Count > 0)
move = moves.WorseMoves[Random.Next(moves.WorseMoves.Count)];
return move;
}
private static (int score, int depth) MinMax(Board _currentBoard, bool isMaximizingPlayer, int alpha, int beta, int depth)
{
var res = _currentBoard.CheckMatchResult();
if (res != Kind.None)
{
var result = (score: -10, depth: depth);
if (res == Kind.Tie)
result.score = 0;
else if (res == AI_type)
result.score = 10;
return result;
}
int max_x = _currentBoard.GetState().GetLength(1);
int max_y = _currentBoard.GetState().GetLength(0);
if (isMaximizingPlayer)
{
var bestResult = (score: Int32.MinValue, depth: Int32.MaxValue);
for (int y = 0; y < max_y; y++)
{
for (int x = 0; x < max_x; x++)
{
if (_currentBoard.SetMove(x, y))
{
var result = MinMax(_currentBoard.Clone(), AI_type == _currentBoard.CurrentPlayer.Type, alpha, beta, depth + 1);
_currentBoard.UndoLastMove();
bestResult = Max(result, bestResult);
alpha = Math.Max(alpha, result.score);
if (beta <= alpha)
return bestResult;
}
}
}
return bestResult;
}
else
{
var bestResult = (score: Int32.MaxValue, depth: Int32.MaxValue);
for (int y = 0; y < max_y; y++)
{
for (int x = 0; x < max_x; x++)
{
if (_currentBoard.SetMove(x, y))
{
var result = MinMax(_currentBoard.Clone(), AI_type == _currentBoard.CurrentPlayer.Type, alpha, beta, depth + 1);
_currentBoard.UndoLastMove();
bestResult = Min(bestResult, result);
beta = Math.Min(beta, result.score);
if (beta <= alpha)
return bestResult;
}
}
}
return bestResult;
}
}
private static (int score, int depth) Max((int score, int depth) result1, (int score, int depth) result2)
{
var res = result1;
if (result1.score > result2.score)
{
res.score = result1.score;
res.depth = result1.depth;
}
if (result2.score > result1.score)
{
res.score = result2.score;
res.depth = result2.depth;
}
if (result1.score == result2.score)
{
res.depth = Math.Min(result1.depth, result2.depth);
}
return res;
}
private static (int score, int depth) Min((int score, int depth) result1, (int score, int depth) result2)
{
var res = result1;
if(result1.score < result2.score) {
res.score = result1.score;
res.depth = result1.depth;
}
if (result2.score < result1.score)
{
res.score = result2.score;
res.depth = result2.depth;
}
if (result1.score == result2.score)
{
res.depth = Math.Min(result1.depth, result2.depth);
}
return res;
}
}
}