TopCoder SRM587: TriangleXor

public class TriangleXor {
    public int theArea(int W) {
        double area = 0;

        // top
        if (W % 2 == 0) area += W / 4.0;

        // side
        double ratio = 0, prevX = 0;
        for (int i = 1; i <= W; i++) {
            double x = 1.0 * i * W / (W + i);

            if (i % 2 == 1) {
                ratio += x - prevX;
            }

            prevX = x;
        }
        area += (W / 4.0) * ratio / (W / 2.0) * 2;

        // bottom
        int num = 1;
        double bottomarea = 0;
        for (int l = 1, r = W; l <= r; l++, r--) {
            double x = (W - l) * 1.0 * (r - l) / (W + r - l) + l;
            double y = 1.0 * (r - l) / W;
            double prevY = 1.0 * (r - l + 1) / (W + r - l + 1);
            double nextY = 1.0 * (r - l - 1) / (W + r - l - 1);
            double dy = prevY - y;
            if (r - l - 1 >= 0) dy += y - nextY;
            double h = x - W / 2.0;
            bottomarea += dy * h * num;
            num += 2;
        }

        if (W % 2 == 0) {
            area += bottomarea;
        } else {
            area += W / 4.0 - bottomarea;
        }
        return (int)area;
    }
}