diffs.js

module.exports = function (diffs) {
    let diffsX = diffs.reduce((acc, [x, y]) => acc + x, 0);
    let diffsY = diffs.reduce((acc, [x, y]) => acc + y, 0);

    if ((diffsX % 2) || (diffsY % 2)) {
        return null;
    }

    diffsX = diffsX / 2;
    diffsY = diffsY / 2;

    return diffs.map(([x, y], pos) => {
        if (x === 1 && diffsX) {
            diffsX--;
            x = -1;
        }

        if (y === 1 && diffsY) {
            diffsY--;
            y = -1;
        }

        return [x, y];
    });
};