SolutionS to Programming PuzzleS
Solutions to Programming Puzzles
Here are the solutions to the programming puzzles at the ends of the chapters. There's not always a single solution to a puzzle, so the one you've come up with may not match what you'll find here, but the examples will give you an idea of possible approaches.
Chapter 3
#1: Favorites
Here's one solution with three favorite hobbies and three favorite foods:
>>> hobbies = ['Pokemon', 'LEGO Mindstorms', 'Mountain Biking'] >>> foods = ['Pancakes', 'Chocolate', 'Apples'] >>> favorites = hobbies + foods >>> print(favorites) ['Pokemon', 'LEGO Mindstorms', 'Mountain Biking', 'Pancakes', 'Chocolate', 'Apples']
#2: Counting Combatants
We can do the calculation in a number of different ways. We have three buildings with 25 ninjas hiding on each roof, and two tunnels with 40 samurai hiding in each. We could work out the total ninjas and then the total samurai, and just add those two numbers together:
>>> 3*25 75 >>> 2*40 80 >>> 75+80 155
Much shorter (and better) is to combine those three equations, using parentheses (the parentheses aren't necessary, due to the order of the mathematical operations, but they make the equation easier to read):
>>> (3*25)+(2*40)
But perhaps a nicer Python program would be something like the following, which tells us what we're calculating:
>>> roofs = 3 >>> ninjas_per_roof = 25 >>> tunnels = 2 >>> samurai_per_tunnel = 40 >>> print((roofs * ninjas_per_roof) + (tunnels * samurai_per_tunnel)) 155
2Solutions for Chapter 3
#3: Greetings!
In this solution, we give the variables meaningful names, and then use format placeholders (%s %s) in our string to embed the values of those variables:
>>> first_name = 'Brando' >>> last_name = 'Ickett' >>> print('Hi there, %s %s!' % (first_name, last_name)) Hi there, Brando Ickett!
Chapter 4
#1: A Rectangle
Drawing a rectangle is almost exactly the same as drawing a square, except that the turtle needs to draw two sides that are longer than the other two:
>>> import turtle >>> t = turtle.Pen() >>> t.forward(100) >>> t.left(90) >>> t.forward(50) >>> t.left(90) >>> t.forward(100) >>> t.left(90) >>> t.forward(50)
#2: A Triangle
The puzzle didn't specify what sort of triangle to draw. There are three types of triangles: equilateral, isosceles, and scalene. Depending on how much you know about geometry, you may have drawn any sort of triangle, perhaps by fiddling with the angles until you ended up with something that looked right.
For this example, let's concentrate on the first two types, because they're the most straightforward to draw. An equilateral triangle has three equal sides and three equal angles:
>>> import turtle >>> t = turtle.Pen() u >>> t.forward(100)
Solutions for Chapter 43
v >>> t.left(120) w >>> t.forward(100) x >>> t.left(120) y >>> t.forward(100)
We draw the base of the triangle by moving forward 100 pixels at u. We turn left 120 degrees (this creates an interior angle of 60 degrees) at v, and again move forward 100 pixels at w. The next turn is also 120 degrees at x, and the turtle moves back to the starting position by moving forward another 100 pixels at y. Here's the result of running the code:
An isosceles triangle has two equal sides and two equal angles:
>>> import turtle >>> t = turtle.Pen() >>> t.forward(50) >>> t.left(104.47751218592992) >>> t.forward(100) >>> t.left(151.04497562814015) >>> t.forward(100)
In this solution, the turtle moves forward 50 pixels, and then turns 104.47751218592992 degrees. It moves forward 100 pixels, followed by a turn of 151.04497562714015 degrees, and then forward 100 pixels again. To turn the turtle back to face its starting position, we can call the following line again:
>>> t.left(104.47751218592992)
4Solutions for Chapter 4
Here's the result of running this code:
How do we come up with angles like 104.47751218592992 degrees and 151.04497562814015 degrees? After all, those are rather obscure numbers!
Once we've decided on the lengths of each of the sides of the triangle, we can calculate the interior angles using Python and a bit of trigonometry. In the following diagram, you can see that if we know the degree of angle a, we can work out the degrees of the (outside) angle b that the turtle needs to turn. The two angles a and b will add up to 180 degrees.
180?
a
b
turtle
It's not difficult to calculate the inside angle if you know the right equation. For example, say we want to create a triangle with a bottom length of 50 pixels (let's call that side C), and two sides A and B, both 100 pixels long.
Solutions for Chapter 45
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