/** Copyright by Barry G. Becker, 2000-2011. Licensed under MIT License: http://www.opensource.org/licenses/MIT */
package com.barrybecker4.game.twoplayer.go.board.analysis.group;
import com.barrybecker4.game.twoplayer.go.board.GoBoard;
import com.barrybecker4.game.twoplayer.go.board.GoProfiler;
import com.barrybecker4.game.twoplayer.go.board.analysis.neighbor.NeighborAnalyzer;
import com.barrybecker4.game.twoplayer.go.board.elements.group.GoGroup;
import com.barrybecker4.game.twoplayer.go.board.elements.group.GoGroupSet;
import com.barrybecker4.game.twoplayer.go.board.elements.position.GoBoardPosition;
import com.barrybecker4.game.twoplayer.go.board.elements.position.GoBoardPositionSet;
import java.util.Set;
/**
* Finds the weakest group on the board relative to some other group.
* @author Barry Becker
*/
class WeakestGroupFinder {
private GoBoard board;
private GroupAnalyzerMap analyzerMap;
/**
* Constructor
*/
public WeakestGroupFinder(GoBoard board, GroupAnalyzerMap analyzerMap) {
this.board = board;
this.analyzerMap = analyzerMap;
}
/**
* Given a set of same color stones, find the weakest enemy group that is bordering it.
* @param groupStones the stones to find the weakest bordering neighbor of.
* Note: we assume that the groupStones all have the same color.
* @return the weakest bordering enemy group. Returns null if no group found.
*/
public GoGroup findWeakestGroup(GoBoardPositionSet groupStones) {
boolean isPlayer1 = groupStones.getOneMember().getPiece().isOwnedByPlayer1();
Set enemyNbrGroups = getEnemyGroupNeighbors(groupStones, isPlayer1);
// we multiply by a +/- sign depending on the side
float side = isPlayer1? 1.0f : -1.0f;
// initialize to strongest value, then anything will be weaker.
double weakestHealth = -side;
GoGroup weakestGroup = null;
for (Object egroup : enemyNbrGroups) {
GoGroup enemyGroup = (GoGroup)egroup;
double h = analyzerMap.getAnalyzer(enemyGroup).getAbsoluteHealth();
if ((side * h) > (side * weakestHealth)) {
weakestHealth = h;
weakestGroup = enemyGroup;
}
}
return weakestGroup;
}
/**
* @@ may need to make this n^2 method more efficient.
* note: has intentional side effect of marking stones with enemy group nbrs as visited (within groupStones).
* @param groupStones the set of stones in the group to find enemies of.
* @return a HashSet of the groups that are enemies of this group
*/
private Set getEnemyGroupNeighbors(GoBoardPositionSet groupStones, boolean isPlayer1) {
GoProfiler.getInstance().startGetEnemyGroupNbrs();
GoGroupSet enemyNbrs = new GoGroupSet();
NeighborAnalyzer nbrAnalyzer = new NeighborAnalyzer(board);
// for every stone in the group.
for (GoBoardPosition stone : groupStones) {
GoBoardPositionSet nbrs = nbrAnalyzer.findGroupNeighbors(stone, false);
addEnemyNeighborsForStone(enemyNbrs, stone, nbrs, isPlayer1);
}
GoProfiler.getInstance().stopGetEnemyGroupNbrs();
return enemyNbrs;
}
/**
* if the stone has any enemy nbrs then mark it visited.
* later we will count how many got visited.
* this is a bit of a hack to determine how surrounded the group is by enemy groups.
* @param enemyNbrs the enemy neighbors to add.
* @param stone stone that enyNbrs are enemy of.
* @param nbrs set of stones to add enemyNbrs to.
*/
private void addEnemyNeighborsForStone(GoGroupSet enemyNbrs, GoBoardPosition stone,
GoBoardPositionSet nbrs, boolean isPlayer1) {
for (GoBoardPosition possibleEnemy : nbrs) {
if (possibleEnemy.getPiece() != null
&& possibleEnemy.getPiece().isOwnedByPlayer1() != isPlayer1
&& !possibleEnemy.isInEye()) {
// setting visited to true to indicate there is an enemy nbr within group distance.
stone.setVisited(true);
// if the group is already there, it does not get added again.
assert (possibleEnemy.getGroup()!=null) : "Possible enemy, "
+ possibleEnemy + ", had no group associated with it!";
enemyNbrs.add(possibleEnemy.getGroup());
}
}
}
}