queens-solver.js

(() => {

var cells = [ ... document.getElementById("queens-grid").querySelectorAll(".queens-cell") ];

var size = Math.sqrt(cells.length);

var map = cells.map(e => e.className.match(/cell-color-(\d+)/)[1]);

var queens = Array(map.length).fill(0);
var colors = map.reduce((a, c) => (a[c]=0, a), {});
var cols = Array(size).fill(0);

var take = (i,j) => { queens[i+j] = 1; cols[j] = 1; colors[map[i+j]] = 1; };
var retr = (i,j) => { queens[i+j] = 0; cols[j] = 0; colors[map[i+j]] = 0; };
var check = (i,j) => {
    return cols[j] == 0
        && (i >= size && j > 0 ? queens[i+j-size-1] == 0 : true)
        && (i >= size && j < size ? queens[i+j-size+1] == 0 : true)
        && colors[map[i+j]] == 0;
};

var solve = (i = 0) => {
    if (i >= map.length) {
        return 1;
    }

    for (var j = 0; j < size; j++) {
        if (check(i, j)) {
            take(i, j);
            if (solve(i + size)) {
                return 1;
            }
            retr(i, j);
        }
    }
    return 0;
};

var placequeen = (n) => {
    ['mousedown', 'mouseup', 'mousedown', 'mouseup'].forEach(ev => {
        cells[n].dispatchEvent(new MouseEvent(ev, { bubbles: true, cancelable: true, }));
    });
};

if (solve())
    queens.forEach((e, i) => e ? placequeen(i) : null);

})();