Find Chess960 starting position identifier: Difference between revisions
Find Chess960 starting position identifier (view source)
Revision as of 12:25, 8 May 2023
, 1 year ago→{{header|Java}}
Line 560:
<syntaxhighlight>
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.function.Predicate;
public final class Chess960SPID {
public static void main(String[] aArgs) {
String[] positions = { "QNRBBNKR", "RNBQKBNR", "RQNBBKRN", "RNQBBKRN" };
createKnightsTable();
for ( String position : positions ) {
validate("RQNBBKRN");
System.out.println("Position " + position + " has Chess960 SP-ID = " + calculateSPID(position));
}
}
private static void validate(String aPosition) {
if ( aPosition.length() != 8 ) {
throw new AssertionError("Chess position has invalid length: " + aPosition.length() + ".");
}
Map<Character, Integer> pieces = new HashMap<Character, Integer>();
for ( char ch : aPosition.toCharArray() ) {
pieces.merge(ch, 1, (oldV, newV) -> oldV + 1);
}
Set<Map.Entry<Character, Integer>> correctPieces =
Set.of(Map.entry('R', 2), Map.entry('N', 2), Map.entry('B', 2), Map.entry('Q', 1), Map.entry('K', 1));
if ( ! pieces.entrySet().equals(correctPieces) ) {
throw new AssertionError("Chess position contains incorrect pieces.");
}
List<Integer> bishops = List.of(aPosition.indexOf('B'), aPosition.lastIndexOf('B'));
if ( ( bishops.get(1) - bishops.get(0) ) % 2 == 0 ) {
throw new AssertionError("Bishops must be on different coloured squares.");
}
List<Integer> rookAndKing = List.of(aPosition.indexOf('R'), aPosition.indexOf('K'), aPosition.lastIndexOf('R'));
if ( ! ( rookAndKing.get(0) < rookAndKing.get(1) && rookAndKing.get(1) < rookAndKing.get(2) ) ) {
throw new AssertionError("The king must be between the two rooks.");
}
}
private static int calculateSPID(String aPosition) {
String noBishopsOrQueen = retainIf(aPosition, s -> s != 'B' && s != 'Q');
final int N = knightsTable.get(List.of(noBishopsOrQueen.indexOf('N'), noBishopsOrQueen.lastIndexOf('N')));
String noBishops = retainIf(aPosition, s -> s != 'B');
final int Q = noBishops.indexOf('Q');
final int indexOne = aPosition.indexOf('B');
final int indexTwo = aPosition.lastIndexOf('B');
final int D = ( indexOne % 2 == 0 ) ? indexOne / 2 : indexTwo / 2;
final int L = ( indexOne % 2 == 0 ) ? indexTwo / 2 : indexOne / 2;
return 96 * N + 16 * Q + 4 * D + L;
}
private static String retainIf(String aText, Predicate<Character> aPredicate) {
return aText.chars().mapToObj(i -> (char) i).filter(aPredicate).map(String::valueOf).reduce("", String::concat);
}
private static void createKnightsTable() {
knightsTable = new HashMap<List<Integer>, Integer>();
knightsTable.put(List.of(0, 1), 0);
knightsTable.put(List.of(0, 2), 1);
knightsTable.put(List.of(0, 3), 2);
knightsTable.put(List.of(0, 4), 3);
knightsTable.put(List.of(1, 2), 4);
knightsTable.put(List.of(1, 3), 5);
knightsTable.put(List.of(1, 4), 6);
knightsTable.put(List.of(2, 3), 7);
knightsTable.put(List.of(2, 4), 8);
knightsTable.put(List.of(3, 4), 9);
}
private static Map<List<Integer>, Integer> knightsTable;
}
</syntaxhighlight>
{{ out }}
<pre>
Position QNRBBNKR has Chess960 SP-ID = 105
Position RNBQKBNR has Chess960 SP-ID = 518
Position RQNBBKRN has Chess960 SP-ID = 601
Position RNQBBKRN has Chess960 SP-ID = 617
</pre>
| |||