// alpha beta with iterative deepening
private static string PerformNearMove(Path shortestPath)
{
int depth = 0;
float time = 0;
float score, bestScore;
GameState gs = new GameState();
Point p = new Point();
// default to something that won't kill us - server sometimes
// runs out of time WAY early resulting in no time to perform alpha beta
// iterations
string bestMove = Map.MOVES[0]; //PerformFoolishRandomMove();
DateTime lastAlphaBeta;
List<string> ties = new List<string>();
string[] moves = new string[4];
float[] scores = new float[4]; // 0 north, 1 south, 2 east, 3 west
scores[0]=3;
scores[1]=2;
scores[2]=1;
scores[3]=0;
// used to adjust time estimate for next depth so we don't go over time limit
float timebase = ((float)Map.Width() * (float)Map.Height()) / (15f * 15f);
while(Duration() + time < (TIME_LIMIT - TIME_THRESHOLD) && depth <= 12) {
score = int.MinValue;
bestScore = int.MinValue;
depth++;
// order moves by previous iterations scores
// TODO this really does nothing. Cache of game states is needed
// for quick eval retrival and move ordering
int length = scores.Length;
bool swapped = true;
moves[0] = "North";
moves[1] = "South";
moves[2] = "East";
moves[3] = "West";
while(swapped) {
swapped = false;
for(int b=0; b<length - 1; b++) {
if (scores[b] < scores[b+1]) {
string tmp = moves[b];
float ftmp = scores[b];
moves[b] = moves[b+1];
scores[b] = scores[b+1];
moves[b+1] = tmp;
scores[b+1] = ftmp;
swapped = true;
}
}
length -= 1;
//Console.Error.WriteLine("best:" + best + " score:" + scores[best]);
}
for(int i=0; i<moves.Length; i++) {
string move = moves[i];
p.X = Map.MyX(); p.Y = Map.MyY();
p.MoveInDirection(move);
if (!Map.IsWall(p.X, p.Y)) {
// negate since starting with opponents moves
lastAlphaBeta = DateTime.Now;
score = -AlphaBeta(gs.ApplyMoveToMeAndCreate(move), depth, -int.MaxValue, -(-int.MaxValue), false);
// estimate time for next depth
TimeSpan ts = DateTime.Now - lastAlphaBeta;
time = (float)ts.Milliseconds * (depth * timebase);
} else {
score = int.MinValue;
}
//Console.Error.WriteLine("alphabeta:" + move + ":" + score + " depth:" + depth);
if (score > bestScore) {
bestMove = move;
bestScore = score;
ties.Clear();
ties.Add(bestMove);
} else if (score == bestScore) {
ties.Add(move);
}
// track score
string temp = move.Substring(0, 1).ToUpper();
int firstChar = (int)temp[0];
switch(firstChar) {
case 'N':
scores[0] = score;
break;
case 'S':
scores[1] = score;
break;
case 'E':
scores[2] = score;
break;
case 'W':
scores[3] = score;
break;
}
}
depth++;
}
List<string> secondaryTies = new List<string>();
// break ties
if (ties.Count > 1) {
bestScore = int.MinValue;
foreach(string move in ties) {
//Console.Error.WriteLine("alpha tie break:" + move);
p.X = Map.MyX(); p.Y = Map.MyY();
p.MoveInDirection(move);
if (Map.IsWall(p.X, p.Y)) {
continue;
}
Territory room = new Territory(gs.ApplyMoveToMeAndCreate(move));
room.DetermineTerritories();
score = (float)room.GetMySize() - (float)room.GetOpponentSize();
//Console.Error.WriteLine("alpha tie break:" + move + ":" + score);
if (score > bestScore) {
bestScore = score;
bestMove = move;
secondaryTies.Clear();
secondaryTies.Add(move);
} else if (score == bestScore) {
secondaryTies.Add(move);
}
}
}
// kinda lame, but need another tie breaker...quick and dirty
if (secondaryTies.Count > 1) {
bestScore = int.MinValue;
foreach(string move in ties) {
if (shortestPath != null) {
if (move.Equals(shortestPath.direction)) {
bestMove = shortestPath.direction;
break;
}
}
p.X = Map.MyX(); p.Y = Map.MyY();
p.MoveInDirection(move);
if (Map.IsWall(p.X, p.Y)) {
continue;
}
score = -GetEuclideanOpponentDistance(p.X, p.Y);
//Console.Error.WriteLine("alpha tie break:" + move + ":" + score);
if (score > bestScore) {
bestScore = score;
bestMove = move;
}
}
}
return bestMove;
}
// Evaluation function for alpha-beta pruning / minimax
private static float EvaluateMove(GameState gs)
{
if (gs.IsMyWin()) {
return MAX_MAP_SIZE;
}
if (gs.IsOpponentWin()) {
return -MAX_MAP_SIZE;
}
if (gs.IsDraw()) {
// return 0
}
Territory room = new Territory(gs);
room.DetermineTerritories();
int mySize = room.GetMySize();
int opponentSize = room.GetOpponentSize();
int size = room.GetMySize() - room.GetOpponentSize();
//Console.Error.WriteLine(String.Format("my room:{0} other room:{1}",mySize,opponentSize));
return (float)size;
}
