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function colourValue(value) {
return value < 4;
}
function parsePosition(str) {
if (str.length != 2) return null;
var a = str.toUpperCase().charCodeAt(0), b = str.charCodeAt(1);
if (a < 65 || a > 65+25) return null;
if (b < 48 || b > 48+9) return null;
return N * (N - (b - 48)) + a - 65;
}
function parseMove(str) {
if (str.length != 5) return null;
if (str[2] != "-" && str[2] != " ") return null;
var from, to;
from = parsePosition(str.substr(0, 2));
if (from != null) {
to = parsePosition(str.substr(3, 2));
if (to != null) {
return {from: from, to: to};
}
}
return null;
}
function stringifyPosition(pos) {
return String.fromCharCode(65 + pos % N) + String.fromCharCode(48 + N - ~~(pos / N));
}
function stringifyMove(mv) {
return stringifyPosition(mv.from) + '-' + stringifyPosition(mv.to);
}
function stringifyMoveExt(mv, captures) {
var s = stringifyMove(mv);
if (captures.length > 0) {
for (var i = 0; i < captures.length; i++) {
s += (i == 0 ? "x" : "/") + stringifyPosition(captures[i]);
}
}
return s;
}
function stoneFlankedH(pos, by) {
if (by & (WHITE|KING)) by = WHITE|KING;
return ((board[pos-1] & by) || (pos-1 == BOARDMID && board[BOARDMID] == EMPTY)) &&
((board[pos+1] & by) || (pos+1 == BOARDMID && board[BOARDMID] == EMPTY));
}
function stoneFlankedV(pos, by) {
if (by & (WHITE|KING)) by = WHITE|KING;
return ((board[pos-N] & by) || (pos-N == BOARDMID && board[BOARDMID] == EMPTY)) &&
((board[pos+N] & by) || (pos+N == BOARDMID && board[BOARDMID] == EMPTY));
}
function kingEncircled(pos) {
if (pos == BOARDMID) {
return board[pos-1] == BLACK && board[pos+1] == BLACK &&
board[pos-N] == BLACK && board[pos+N] == BLACK;
} else if (pos == BOARDMID-1) {
return board[pos-1] == BLACK && board[pos-N] == BLACK && board[pos+N] == BLACK;
} else if (pos == BOARDMID+1) {
return board[pos+1] == BLACK && board[pos-N] == BLACK && board[pos+N] == BLACK;
} else if (pos == BOARDMID-N) {
return board[pos-1] == BLACK && board[pos+1] == BLACK && board[pos-N] == BLACK;
} else if (pos == BOARDMID+N) {
return board[pos-1] == BLACK && board[pos+1] == BLACK && board[pos+N] == BLACK;
} else {
var x = pos % N, y = ~~(pos / N);
return (x > 0 && x < N-1 && board[pos-1] == BLACK && board[pos+1] == BLACK) ||
(y > 0 && y < N-1 && board[pos-N] == BLACK && board[pos+N] == BLACK);
}
}
function applyMove(mv) {
board[mv.to] = board[mv.from];
board[mv.from] = EMPTY;
var i = mv.to;
var x = i % N, y = ~~(i / N);
var captures = [];
if (x > 1 && board[i-1] != EMPTY && colourValue(board[i-1]) != colourValue(board[i])) {
if (board[i-1] == KING ? kingEncircled(i-1) : stoneFlankedH(i-1, board[i])) {
board[i-1] = EMPTY;
captures.push(i-1);
}
}
if (y > 1 && board[i-N] != EMPTY && colourValue(board[i-N]) != colourValue(board[i])) {
if (board[i-N] == KING ? kingEncircled(i-N) : stoneFlankedV(i-N, board[i])) {
board[i-N] = EMPTY;
captures.push(i-N);
}
}
if (x < N-2 && board[i+1] != EMPTY && colourValue(board[i+1]) != colourValue(board[i])) {
if (board[i+1] == KING ? kingEncircled(i+1) : stoneFlankedH(i+1, board[i])) {
board[i+1] = EMPTY;
captures.push(i+1);
}
}
if (y < N-2 && board[i+N] != EMPTY && colourValue(board[i+N]) != colourValue(board[i])) {
if (board[i+N] == KING ? kingEncircled(i+N) : stoneFlankedV(i+N, board[i])) {
board[i+N] = EMPTY;
captures.push(i+N);
}
}
return captures;
}
function checkWin() {
for (var x = 0; x < N; x++) if (board[x] == KING) return 1;
for (var y = 0; y < N; y++) if (board[N * y] == KING) return 1;
for (var x = 0; x < N; x++) if (board[N * (N-1) + x] == KING) return 1;
for (var y = 0; y < N; y++) if (board[N * y + N-1] == KING) return 1;
for (var i = 0; i < N * N; i++) {
if (board[i] == KING) return 0;
}
return -1;
}
function isValid(mv) {
if (mv.from < 0 || mv.from >= N * N || mv.to < 0 || mv.to >= N * N) return false;
if (mv.from == mv.to) return false;
if (board[mv.from] == EMPTY || board[mv.to] != EMPTY) return false;
if (mv.to == BOARDMID) return false;
var x1 = mv.from % N, y1 = ~~(mv.from / N);
var x2 = mv.to % N, y2 = ~~(mv.to / N);
if (x1 != x2 && y1 != y2) return false;
if (x1 == x2) {
var delta = y2 < y1 ? -1 : 1;
for (var y = y1 + delta; y != y2; y += delta) {
if (board[N * y + x1] != EMPTY) return false;
}
} else {
var delta = x2 < x1 ? -1 : 1;
for (var x = x1 + delta; x != x2; x += delta) {
if (board[N * y1 + x] != EMPTY) return false;
}
}
return true;
}
function isValidForPlayer(mv, player) {
var mask = player == 1 ? WHITE|KING : BLACK;
return isValid(mv) && (board[mv.from] & mask) != 0;
}
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