Code to fit a rectangle inside another rectangle while keeping aspect ratio.

FitRectangleInRectangle.java

public final class FitRectangleInRectangle {

    public static class Input {

        public int height;

        public int width;

        public Input() {}

        public Input(int width, int height) {
            this.width = width;
            this.height = height;
        }
    }

    public static class Output extends Input {

        public double scale;

        @Override
        public String toString() {
            return String.format("{width: %s, height: %s, scale: %s}",
             width, height, scale);
        }

        public Output() {}

        public Output(int width, int height, double scale) {
            super(width, height);
            this.scale = scale;
        }
    }

    public static final Output fitRectangleInRectangle(Input inner, Input outer) {
        Output output = new Output();
        if ((inner == null) || (outer == null)) {
            return null;
        }
        double innerAspectRatio = ((double) inner.width) / ((double) inner.height);
        double outerAspectRatio = ((double) outer.width) / ((double) outer.height);
        if (innerAspectRatio < outerAspectRatio) {
            output.scale = ((double) outer.height) / ((double) inner.height);
        } else {
            output.scale = ((double) outer.width) / ((double) inner.width);
        }
        output.width  = (int) Math.round(output.scale * ((double) inner.width ));
        output.height = (int) Math.round(output.scale * ((double) inner.height));
        return output;
    }

    public static void main(String[] args) {
        System.out.println(fitRectangleInRectangle(new Input(500, 250), new Input(200, 50)));
        System.out.println(fitRectangleInRectangle(new Input(250, 200), new Input(200, 50)));
    }
}

/*
TODO permute possibilites to make test cases

ratio inner ? outer
<
=
>

size inner ? outer (completely contain or be contained to make it easier at first)
<
=
>

inner aspect ratio
horizontal
square
vertical

outer aspect ratio
horizontal
square
vertical
*/