Compute intersection of two identical objects

Question

I've got 2 Rectangles, both have the same edges.

new Rectangle(Arrays.asList(new Coord(1,1), new Coord(2,1), new Coord(2,2), new Coord(1,2)));

From my understanding the Intersection should be 1, however my function returns -1.

public Rectangle(List<Coord> edges){
        Assert.assertTrue("Provide an exact number of 4 edges", edges.size() == 4);
        this.edges = edges;
        left = getLeft(edges);
        right = getRight(edges);
        top = getTop(edges);
        bottom = getBottom(edges);
    }

private static int computeIntersection(Rectangle rect1, Rectangle rect2){

        int x_overlap = Math.min(rect1.right, rect2.right) - Math.max(rect1.left, rect2.left);
        int y_overlap = Math.min(rect1.bottom,rect2.bottom) - Math.max(rect1.top,rect2.top);
        System.out.println(x_overlap * y_overlap);


        return x_overlap * y_overlap;

    }

Do I have a problem with my math there, when computing the intersection or what did I not consider?

Answer 1

First, you should check if the two rectangle is actually overlapped or not.

And, you should use the min top substract the max bottom.

private static int computeIntersection(Rectangle rect1, Rectangle rect2){
    if (rect1.left >= rect2.right || rect2.left >= rect1.right
            || rect1.bottom >= rect2.top || rect2.bottom >= rect1.top) {
        return 0;
    } else {
        int x_overlap = Math.min(rect1.right, rect2.right) - Math.max(rect1.left, rect2.left);
        int y_overlap = Math.min(rect1.top,rect2.top) - Math.max(rect1.bottom,rect2.bottom);
        return x_overlap * y_overlap;
    }
}