8-queen test

8-queen.js

// Run online at:
// https://algorithm-pad.now.sh/?gist=https://gist.githubusercontent.com/huytd/d9c162e8d6392c39595395521896c028/raw/343c11a97c8edc5538ae88a3144e754be1162a74/8-queen.js

board = [
    [0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, 0],
]

debug(board)

const nextAvailable = () => {
    for (let i = 0; i < board.length; i++) {
        for (let j = 0; j < board.length; j++) {
            if (board[i][j] === 0) return [i, j];
        }
    }
    return false;
}

const placeQueen = (y, x) => {
    if (board[y][x] === 0) {
        board[y][x] = '*';
    } else {
        return false;
    }
    let i; let j;
    // north
    i = y - 1; j = x;
    while (i >= 0) {
        if (board[i][j] !== '*') {
            board[i][j] = ' ';
            i--;
        } else {
            return false;
        }
    }
    // south
    i = y + 1; j = x;
    while (i < board.length) {
        if (board[i][j] !== '*') {
            board[i][j] = ' ';
            i++;
        } else {
            return false;
        }
    }
    // west
    i = y; j = x - 1;
    while (j >= 0) {
        if (board[i][j] !== '*') {
            board[i][j] = ' ';
            j--;
        } else {
            return false;
        }
    }
    // east
    i = y; j = x + 1;
    while (j < board.length) {
        if (board[i][j] !== '*') {
            board[i][j] = ' ';
            j++;
        } else {
            return false;
        }
    }
    // north west
    i = y - 1; j = x - 1;
    while (i >= 0 && j >= 0) {
        if (board[i][j] !== '*') {
            board[i][j] = ' ';
            i--; j--;
        } else {
            return false;
        }
    }
    // south west
    i = y + 1; j = x - 1;
    while (i < board.length && j >= 0) {
        if (board[i][j] !== '*') {
            board[i][j] = ' ';
            i++; j--;
        } else {
            return false;
        }
    }
    // south east
    i = y + 1; j = x + 1;
    while (i < board.length && j < board.length) {
        if (board[i][j] !== '*') {
            board[i][j] = ' ';
            i++; j++;
        } else {
            return false;
        }
    }
    // north east
    i = y - 1; j = x + 1;
    while (i >= 0 && j < board.length) {
        if (board[i][j] !== '*') {
            board[i][j] = ' ';
            i--; j++;
        } else {
            return false;
        }
    }
    return true;
}

const removeQueen = (y, x) => {
    board[y][x] = 0;
    let i; let j;
    // north
    i = y - 1; j = x;
    while (i >= 0) {
        board[i][j] = 0;
        i--;
    }
    // south
    i = y + 1; j = x;
    while (i < board.length) {
        board[i][j] = 0;
        i++;
    }
    // west
    i = y; j = x - 1;
    while (j >= 0) {
        board[i][j] = 0;
        j--;
    }
    // east
    i = y; j = x + 1;
    while (j < board.length) {
        board[i][j] = 0;
        j++;
    }
    // north west
    i = y - 1; j = x - 1;
    while (i >= 0 && j >= 0) {
        board[i][j] = 0;
        i--; j--;
    }
    // south west
    i = y + 1; j = x - 1;
    while (i < board.length && j >= 0) {
        board[i][j] = 0;
        i++; j--;
    }
    // south east
    i = y + 1; j = x + 1;
    while (i < board.length && j < board.length) {
        board[i][j] = 0;
        i++; j++;
    }
    // north east
    i = y - 1; j = x + 1;
    while (i >= 0 && j < board.length) {
        board[i][j] = 0;
        i--; j++;
    }
}

placeQueen(2, 3);
let cell = nextAvailable();
while (cell) {
    let [y, x] = cell;
    let ok = placeQueen(y, x);
    if (ok) {
        cell = nextAvailable();
    } else {
        removeQueen(y, x);
    }
}

debug(board);