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    <p>A bounding box is usually a rectangle. I don't think a circle located at (-r,-r) is the bounding box of a circle of radius r....</p> <p>Anyway, suppose you have a bounding box b1 and another b2 and a function <code>combineBoxes</code> that computes the bounding box of b1 and b2.</p> <p>Then if you have a <em>non-empty</em> set of shapes in your group, you can use <code>reduceLeft</code> to compute the whole bounding box of a list of bounding boxes by combining them two at a time until only one giant box remains. (The same idea can be used to reduce a list of numbers to a sum of numbers by adding them in pairs. And it's called <code>reduceLeft</code> because it works left to right across the list.)</p> <p>Suppose that <code>blist</code> is a list of bounding boxes of each shape. (Hint: this is where <code>map</code> comes in.) Then</p> <pre><code>val bigBox = blist reduceLeft( (box1,box2) =&gt; combineBoxes(box1,box2) ) </code></pre> <p>You'll need to catch the empty group case separately, however. (Since it has a no well-defined bounding box, you don't want to use folds; folds are good for when there is a default empty case that makes sense. Or you have to fold with <code>Option</code>, but then your combining function has to understand how to combine <code>None</code> with <code>Some(box)</code>, which is probably not worth it in this case--but very well might be if you were writing production code that needs to elegantly handle various sorts of empty list situations.)</p>
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    1. POFunctional programming, Scala map and fold left
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    1. COYour problem does not only seem to be that you don't know the Scala syntax. First, figure out what should happen mathematically. Then worry about how to write it down it the language. Using the correct syntax to do the wrong thing isn't helpful! You need a function or method that can take two bounding boxes and input and produce the bounding box of the two as output. `A.x + R.x` isn't going to put the corner where you want it. If you draw a picture and figure out the math, you're most of the way there.
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