package aima.core.environment.nqueens;
import java.util.ArrayList;
import java.util.List;
import aima.core.util.datastructure.XYLocation;
/**
* Represents a quadratic board with a matrix of squares on which queens can be
* placed (only one per square) and moved.
*
* @author Ravi Mohan
* @author R. Lunde
*/
public class NQueensBoard {
/**
* X---> increases left to right with zero based index Y increases top to
* bottom with zero based index | | V
*/
int[][] squares;
int size;
public NQueensBoard(int n) {
size = n;
squares = new int[size][size];
for (int i = 0; i < size; i++) {
for (int j = 0; j < size; j++) {
squares[i][j] = 0;
}
}
}
public void clear() {
for (int i = 0; i < size; i++) {
for (int j = 0; j < size; j++) {
squares[i][j] = 0;
}
}
}
public void setBoard(List<XYLocation> al) {
clear();
for (int i = 0; i < al.size(); i++) {
addQueenAt(al.get(i));
}
}
public int getSize() {
return size;
}
public void addQueenAt(XYLocation l) {
if (!(queenExistsAt(l)))
squares[l.getXCoOrdinate()][l.getYCoOrdinate()] = 1;
}
public void removeQueenFrom(XYLocation l) {
if (squares[l.getXCoOrdinate()][l.getYCoOrdinate()] == 1) {
squares[l.getXCoOrdinate()][l.getYCoOrdinate()] = 0;
}
}
/**
* Moves the queen in the specified column (x-value of <code>l</code>) to
* the specified row (y-value of <code>l</code>). The action assumes a
* complete-state formulation of the n-queens problem.
*
* @param l
*/
public void moveQueenTo(XYLocation l) {
for (int i = 0; i < size; i++)
squares[l.getXCoOrdinate()][i] = 0;
squares[l.getXCoOrdinate()][l.getYCoOrdinate()] = 1;
}
public void moveQueen(XYLocation from, XYLocation to) {
if ((queenExistsAt(from)) && (!(queenExistsAt(to)))) {
removeQueenFrom(from);
addQueenAt(to);
}
}
public boolean queenExistsAt(XYLocation l) {
return (queenExistsAt(l.getXCoOrdinate(), l.getYCoOrdinate()));
}
private boolean queenExistsAt(int x, int y) {
return (squares[x][y] == 1);
}
public int getNumberOfQueensOnBoard() {
int count = 0;
for (int i = 0; i < size; i++) {
for (int j = 0; j < size; j++) {
if (squares[i][j] == 1)
count++;
}
}
return count;
}
public List<XYLocation> getQueenPositions() {
ArrayList<XYLocation> result = new ArrayList<XYLocation>();
for (int i = 0; i < size; i++) {
for (int j = 0; j < size; j++) {
if (queenExistsAt(i, j))
result.add(new XYLocation(i, j));
}
}
return result;
}
public int getNumberOfAttackingPairs() {
int result = 0;
for (XYLocation location : getQueenPositions()) {
result += getNumberOfAttacksOn(location);
}
return result / 2;
}
public int getNumberOfAttacksOn(XYLocation l) {
int x = l.getXCoOrdinate();
int y = l.getYCoOrdinate();
return numberOfHorizontalAttacksOn(x, y)
+ numberOfVerticalAttacksOn(x, y)
+ numberOfDiagonalAttacksOn(x, y);
}
public boolean isSquareUnderAttack(XYLocation l) {
int x = l.getXCoOrdinate();
int y = l.getYCoOrdinate();
return (isSquareHorizontallyAttacked(x, y)
|| isSquareVerticallyAttacked(x, y) || isSquareDiagonallyAttacked(
x, y));
}
private boolean isSquareHorizontallyAttacked(int x, int y) {
return numberOfHorizontalAttacksOn(x, y) > 0;
}
private boolean isSquareVerticallyAttacked(int x, int y) {
return numberOfVerticalAttacksOn(x, y) > 0;
}
private boolean isSquareDiagonallyAttacked(int x, int y) {
return numberOfDiagonalAttacksOn(x, y) > 0;
}
private int numberOfHorizontalAttacksOn(int x, int y) {
int retVal = 0;
for (int i = 0; i < size; i++) {
if ((queenExistsAt(i, y)))
if (i != x)
retVal++;
}
return retVal;
}
private int numberOfVerticalAttacksOn(int x, int y) {
int retVal = 0;
for (int j = 0; j < size; j++) {
if ((queenExistsAt(x, j)))
if (j != y)
retVal++;
}
return retVal;
}
private int numberOfDiagonalAttacksOn(int x, int y) {
int retVal = 0;
int i;
int j;
// forward up diagonal
for (i = (x + 1), j = (y - 1); (i < size && (j > -1)); i++, j--) {
if (queenExistsAt(i, j))
retVal++;
}
// forward down diagonal
for (i = (x + 1), j = (y + 1); ((i < size) && (j < size)); i++, j++) {
if (queenExistsAt(i, j))
retVal++;
}
// backward up diagonal
for (i = (x - 1), j = (y - 1); ((i > -1) && (j > -1)); i--, j--) {
if (queenExistsAt(i, j))
retVal++;
}
// backward down diagonal
for (i = (x - 1), j = (y + 1); ((i > -1) && (j < size)); i--, j++) {
if (queenExistsAt(i, j))
retVal++;
}
return retVal;
}
@Override
public int hashCode() {
List<XYLocation> locs = getQueenPositions();
int result = 17;
for (XYLocation loc : locs) {
result = 37 * loc.hashCode();
}
return result;
}
@Override
public boolean equals(Object o) {
if (this == o)
return true;
if ((o == null) || (this.getClass() != o.getClass()))
return false;
NQueensBoard aBoard = (NQueensBoard) o;
boolean retVal = true;
List<XYLocation> locs = getQueenPositions();
for (XYLocation loc : locs) {
if (!(aBoard.queenExistsAt(loc)))
retVal = false;
}
return retVal;
}
public void print() {
System.out.println(getBoardPic());
}
public String getBoardPic() {
StringBuffer buffer = new StringBuffer();
for (int row = 0; (row < size); row++) { // row
for (int col = 0; (col < size); col++) { // col
if (queenExistsAt(col, row))
buffer.append(" Q ");
else
buffer.append(" - ");
}
buffer.append("\n");
}
return buffer.toString();
}
@Override
public String toString() {
StringBuffer buf = new StringBuffer();
for (int row = 0; row < size; row++) { // rows
for (int col = 0; col < size; col++) { // columns
if (queenExistsAt(col, row))
buf.append('Q');
else
buf.append('-');
}
buf.append("\n");
}
return buf.toString();
}
}