Question

I have a table with 8 <tr>s, each with 8 <td>s, each with a data-x value and data-y value of between one and eight, i.e. an 8×8 grid for a chessboard.

Given that bishops can only move diagonally and I have the coordinates of the starting and ending squares, what is the most efficient way to find all the <td> elements in the ‘path’.

Example:

// coordinates representing a bishop move from d6 (4, 6) to h2 (8, 2)
var from = {
    x: 4,
    y: 6
},
to = {
    x: 8,
    y: 2
}

// code to select squares e5 (5,5), f4 (6,4) and g3 (7,3)

How could I select these elements:

td[data-x="5"][data-y="5"],
td[data-x="6"][data-y="4"],
td[data-x="7"][data-y="3"]

in the most efficient way, baring in mind the from and to are set dynamically?

For information, I have written a function used elsewhere to check if the bishop has moved diagonally to start with:

function is_valid_bishop_move(from, to){
    var tan_theta = (to.y - from.y) / (to.x - from.x);
    if( tan_theta === 1 || tan_theta === -1 ){
        return true;
    }else{
        return false;
    }
}

Answer 1

I can only think of something like this:

var from = {
    x: 4,
    y: 6
},
to = {
    x: 8,
    y: 2
}

var delta_x = (to.x - from.x > 0 ? 1 : -1),
    delta_y = (to.y - from.y > 0 ? 1 : -1),
    dest_x = from.x + delta_x,
    dest_y = from.y + delta_y,
    selector = '';

while (dest_x != to.x) {
    selector += 'td[data-x="' + dest_x + '"][data-y="' + dest_y + '"],';
    dest_x += delta_x;
    dest_y += delta_y;
}

selector = selector.replace(/,$/, '');

console.log(selector);
​

http://jsfiddle.net/zerkms/gtEwV/1/