w1d3

Question 1

What’s a good way to visualize ruby’s modulo arithmetic?

Answer 1

Imagine a wheel with numbers written clockwise.

Count clockwise around the wheel for positive modulo.

Count counter-clockwise for negative modulo.

Question 2

What’s a good way to get better debug information from an object?

Answer 2

Override the #inspect method

Question 3

What’s a benefit to using a recursive solution over an iterative solution?

Answer 3

It can be easier to prove the correctness of a recursive algorithm.

Question 4

High-level: quicksort

Recursive or iterative?

Answer 4

Choose a pivot.

Place all items less than the pivot to the left of the pivot.

Place all items greater than the pivot to the right of the pivot.

left = quicksort the left side
right = quicksort the right side

Put these back in order:
left + pivot + right

(it’s recursive)

Question 5

What’s a common cause of a StackOverflowError ?

Answer 5

Broken base case in recursive call

Question 6

What’s the name of the highest level stack frame?

Answer 6

main

Question 7

How do you refer to the smaller and smaller-sized problems that a recursive algorithm breaks its input into?

Answer 7

subproblems

Question 8

What type of mathematical proof lends itself to recursion?

Answer 8

mathematical induction

Question 9

What type of function lends itself to mathematical induction?

Answer 9

recursion

Question 10

What’s mathematical induction in a nutshell?

Answer 10

If we can solve for a base case and we can solve for a general (or nth) case, then we have solved for all the cases.

Question 11

List a 5 step process for programming recursively

Answer 11

Map out a recursive decomposition.

Identify the base case(s).

Think one level up from the base case.

Ensure that the return values from all cases are always of the same type.

Get a stack trace (debuggin).

Question 12

How do you change the number of recursive calls Ruby will allow?

Answer 12

MAX_STACK_SIZE = num

Question 13

What does MAX_STACK_SIZE let you control?

Answer 13

The maximum number of recursive calls allowed.

Question 14

What are some semantic HTML5 containers?

0-2: 1 star
3-4: 2 star
5-6: 3 star
6-7: 4 star
8-9: 5 star

Answer 14

header
fooder
nav
article
aside
figure
figcaption
section
div

Question 15

How does rails use the method_missing function?

Answer 15

dynamic finders such as

User.find_by_username_and_state(‘bob’, ‘california’)

Question 16

Why would you use an underscore as a block argument?

Answer 16

Readability. To indicate to future users of the code not to care about that argument.

Question 17

Consider this code:

x = 7

def foo(x)
  x = 10
end

foo(x)
p x

What value is displayed? Why?

Answer 17

7. The x within the foo method is a new local variable, separate from the x defined on the first line.

Question 18

Why does Enumerable#each return its receiver?

Answer 18

Each is intended to be used solely for its side effects.

Question 19

What’s the difference between:

a = "hello" ; a << "!"
a = "hello" ; a += "!"

Answer 19

The first one mutates the string by pushing a new object onto the end.

The second one reassigns the a pointer to point to a new string.

Question 20

How do you access the last result in pry?

Answer 20

_ (underscore)

Question 21

What does the & operator do in a method definition?

Answer 21

Converts a block into a proc

Proc-ifies a block.

Question 22

What does the & operator do in a method call?

Answer 22

Converts a proc into a block.

Block-ifies a proc.

Question 23

How do you pass a proc to a method that expects a block?

Answer 23

Use the & operator to toggle the proc back into a block.

Question 24

What’s the proper way to set up a new hash that stores mutable objects?

Answer 24

hash = Hash.new { |hash, key| hash[key] = }

Question 25

Why is it useful to use reader/writers internally within a class?

Answer 25

It prevents typos from generating new instance methods. Instead, they generate NoMethodError’s.

self.lmonade throws error
@lmonade creates new instance var

Question 26

How do you look at the class methods native to a class? How about instance methods?

Answer 26

class.methods - Object.methods

instance_of_class.methods - Object.methods

Question 27

Where can you use & to blockify a proc?

Answer 27

In a method call.

Question 28

Where can you use & to procify a block?

Answer 28

In a method definition

Question 29

If a block is passed into a method (as a block, not a proc), what is the only way to call it?

Answer 29

yield