w1d3 Flashcards
What’s a good way to visualize ruby’s modulo arithmetic?
Imagine a wheel with numbers written clockwise.
Count clockwise around the wheel for positive modulo.
Count counter-clockwise for negative modulo.
What’s a good way to get better debug information from an object?
Override the #inspect method
What’s a benefit to using a recursive solution over an iterative solution?
It can be easier to prove the correctness of a recursive algorithm.
High-level: quicksort
Recursive or iterative?
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)
What’s a common cause of a StackOverflowError ?
Broken base case in recursive call
What’s the name of the highest level stack frame?
main
How do you refer to the smaller and smaller-sized problems that a recursive algorithm breaks its input into?
subproblems
What type of mathematical proof lends itself to recursion?
mathematical induction
What type of function lends itself to mathematical induction?
recursion
What’s mathematical induction in a nutshell?
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.
List a 5 step process for programming recursively
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).
How do you change the number of recursive calls Ruby will allow?
MAX_STACK_SIZE = num
What does MAX_STACK_SIZE let you control?
The maximum number of recursive calls allowed.
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
header fooder nav article aside figure figcaption section div
How does rails use the method_missing function?
dynamic finders such as
User.find_by_username_and_state(‘bob’, ‘california’)
Why would you use an underscore as a block argument?
Readability. To indicate to future users of the code not to care about that argument.
Consider this code:
x = 7
def foo(x) x = 10 end
foo(x)
p x
What value is displayed? Why?
- The x within the foo method is a new local variable, separate from the x defined on the first line.
Why does Enumerable#each return its receiver?
Each is intended to be used solely for its side effects.
What’s the difference between:
a = "hello" ; a << "!" a = "hello" ; a += "!"
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.
How do you access the last result in pry?
_ (underscore)
What does the & operator do in a method definition?
Converts a block into a proc
Proc-ifies a block.
What does the & operator do in a method call?
Converts a proc into a block.
Block-ifies a proc.
How do you pass a proc to a method that expects a block?
Use the & operator to toggle the proc back into a block.
What’s the proper way to set up a new hash that stores mutable objects?
hash = Hash.new { |hash, key| hash[key] = }
Why is it useful to use reader/writers internally within a class?
It prevents typos from generating new instance methods. Instead, they generate NoMethodError’s.
self.lmonade throws error
@lmonade creates new instance var
How do you look at the class methods native to a class? How about instance methods?
class.methods - Object.methods
instance_of_class.methods - Object.methods
Where can you use & to blockify a proc?
In a method call.
Where can you use & to procify a block?
In a method definition
If a block is passed into a method (as a block, not a proc), what is the only way to call it?
yield
