Ruby

Front 1

What is a data structure?

Back 1

A data structure is a way of organzing data in a computer so it can be used effectively to retrieve data. It consists out of a pointer and a data record.

Front 2

What is a stack?

Back 2

Data structure where elements are ordered by insertion order. Can only be removed and added to the top. Analogy: Stack of books. Ex: Undo button

Front 3

What is a queue?

Back 3

Data structure where elements are ordered by insertion order. Can only be removed from the front and added to the back. Analogy: Line in theater. Ex: Printer

Front 4

What's the difference between a stack and a queue?

Back 4

The point which can be added upon (queue = back and stack = top) and the point from which can be taken from (queue = front and stack = top)

Front 5

What's the best way to implement stacks and queues in Ruby?

Back 5

Use an array and limit yourself to the required behavior. Using push / pop gives LIFO(last in first out) behavior (stack), while using push / shift gives FIFO behavior (queue)

Front 6

Why bother having many different search algorithms?

Back 6

It can make a big difference in performance depending on the dataset you’re using.

Front 7

What is breadth-first-search (BFS)?

Back 7

A way of navigating a dataset (tree) by level first

Front 8

What is depth-first-search (DFS)? And which types can you use?

Back 8

A way of navigating a dataset (tree) by traversing the nodes and their respective children first. Data,left,right (preorder). Left,data,right (inorder). Left,right,data (postorder)

Front 9

What situations would you want to use BFS?

Back 9

If the tree is very deep and search nodes are rare. depth first search (DFS) might take an extremely long time. If you know a search node is not far from the root of the tree, a breadth first search (BFS) might be better. (get oldest deceased people from family tree & friend suggestions in facebook)

Front 10

What situations would you want to use DFS instead?

Back 10

If the tree is very wide, a BFS might need too much memory, so it might be completely impractical. (youngest still alive person from family tree).

Front 11

When would BFS be impractical?

Back 11

If nodes are frequent but located deep in the tree, BFS could be impractical.

Front 12

What is recursion?

Back 12

Recursion is the idea that a function calls itself. Pretty simple, right? It's used to take a big problem and start breaking it down into smaller and smaller pieces ("Divide and Conquer") and continuing to feed their solutions back into the original function until some sort of answer is achieved and the whole chain unwinds.

Front 13

What are the limitations of using recursive solutions?

Back 13

It uses overall more memory than looping since each recursion copies the result of the previous calculation.

Front 14

What types of problems are more suited for simple loops than recursion?

Back 14

Generally speaking, All. Loops may achieve a performance gain for your program. Recursion may achieve a performance gain for your programmer since the code is shorter and ‘cleaner’.

Front 15

What is meant by "recursive depth?"

Back 15

The distance from the required solution compared to the end case.

Front 16

What is a "stack overflow”?

Back 16

A process going outside of the allotted memory to the task.

Front 17

Why is 'stack overflow' relevant to a recursive problem?

Back 17

Recursion without end case cause infinite loops, which drains memory really quickly.

Front 18

What is an algorithm?

Back 18

A set of consecutive instructions to reach a predefined outcome. Commonly used in sorting and searching data. Ex: pathfinding, querying,

Front 19

What is pseudo-code?

Back 19

Written down steps which logically depict the coding steps in human language. Ex: “Let grandma ask for the time until you shout in all caps”

Front 20

How do you issue an HTTP request in Ruby?

Back 20

Front 21

What is REST

Back 21

Represential state transfer is used to map http actions (get, post, patch and delete) to database actions (create, read, update, delete)

Front 22

What's the difference between a GET and a POST request?

Back 22

A get request asks for a file from the server whilst a post request tries to modify/create a file on the server

Front 23

How do you create, read, update and delete normal files from your computer as a ruby object (and csv’s) and how do you make new files/change/make directories?

Back 23

Front 24

Why do we serialize data?

Back 24

Saving any file as flat data so it can be transferred over the internet.

Front 25

What is JSON?

Back 25

JSON (JavaScript Object Notation) is a minimal, readable format for structuring data. It is used primarily to transmit data between a server and web application, as an alternative to XML.

Front 26

What is YAML?

Back 26

YAML is a flexible, human readable file format that is ideal for storing object trees. YAML stands for “YAML Ain't Markup Language”. It is easier to read (by humans) than JSON, and can contain richer meta data. It is far nicer than XML

Front 27

How do you turn a Ruby object into JSON and back? Difference between generate/to_json/pretty_generate?

Back 27

to_json accepts also non-json objects whilst generate is more strict. Pretty print includes newlines to debug in the command line

Front 28

What is an implicit return?

Back 28

The last evaluation of a function is automatically returned

Front 29

What is a class and what is an instance?

Back 29

A class is an object “mold” for creating similar instances of the class. They predefine the similar functionality and starting variables. An instance is an object based on the class type. Example: Post class and post1 = Post.create(title: “title”, author: “simon”). Like the mold of a sword and a cast

Front 30

When should you use a class?

Back 30

A class should be used when objects need to be instantiated. If it’s just stand-alone functionality, you should use a module.

Front 31

How do you create a class in your script file and what should happen in the initialize method?

Back 31

Front 32

What is a class method and how does it differ from an instance method?

Back 32

A class method is a function which is called on the class itself (ex: self.all = Post.all). An instance method is called on the instance of the class (post1.change_title(“title”)

Front 33

What are the four types of variables in ruby?

Back 33

Front 34

What are "getter" and "setter" methods used for?

Back 34

It means some instance variables can be read and set after instantiation with attr_accessor, attr_reader and attr_writer.

Front 35

How does inheritance work?

Back 35

Allows to inherit functionality and variables. class Dog < Animal

Front 36

Why is inheritance really useful?

Back 36

It allows DRY and create different objects with similar functionality and properties without re-writing everything.

Front 37

How do you require, include and extend a module? How do you extend a class? What does that mean?

Back 37

Front 38

What does #super do?

Back 38

returns the output of the inherited class method

Front 39

What is a "boolean"?

Back 39

true or false operator

Front 40

What are "truthy" values?

Back 40

values that evaluate to true

Front 41

Are nil, 0, "0", "", 1, [], {} and -1 considered true or false?

Back 41

Only nil and false are evaluated to false in ruby

Front 42

When do you use unless?

Back 42

When you want the code to run only if the condition evaluates to false

Front 43

What does <=> do?

Back 43

It compares the first value with the second. It return 0 if equal and 1 if the first one is greater and -1 if the first one is smaller.

Front 44

What do || and && and ! do?

Back 44

Or, and & not

Front 45

What is returned by puts("woah") || true?

Back 45

“woah” Only the first parts gets evaluated in an OR statement. If this returns true, the second isn’t checked.

Front 46

What is ||=?

Back 46

Conditional assignment. It’ll only evaluate the function if the assigned element doesn’t already exist

Front 47

What is the ternary operator?

Back 47

Shorthand version of an if-else statement (condition ? Case if true : case if false)

Front 48

When should you use a case statement?

Back 48

When you have multiple, nested if-else statements

Front 49

What does loop, while, for, each and times do?

Back 49

A for x in @collection is the same as an each loop, but the last x variable persists after the loop. A loop do is the same as while(true). Used when unsure how long it will last but clear when it should end

Front 50

How do you stop a loop?

Back 50

break or exit

Front 51

How do you skip to the next iteration of a loop?

Back 51

next

Front 52

How would you start the loop over again?

Back 52

retry restarts the entire loop. Redo restarts the current loop.

Front 53

What is a block, proc, lambda and what does yield do. How do you call a proc (2 ways)?

Back 53

Front 54

What does #each do?

Back 54

Executes code for each element in argument. Returns one element each iteration.

Front 55

What does #map do?

Back 55

Returns an array where code has been executed for each element in argument.

Front 56

What is the difference between #map and #collect?

Back 56

None

Front 57

What does #select do?

Back 57

Returns an array for each element in argument which matches criteria.

Front 58

What does #inject do?

Back 58

Adds element to index. arr = [a,b,c] arr.inject(1, q). Inserts q at index 1.

Front 59

What does #shift (n) do?

Back 59

Removes first n elements from collection and returns it.

Front 60

What does #pop(n) do?

Back 60

Removes last n elements from collection and returns is.

Front 61

what does #divmod do?

Back 61

Returns quotient and modulus 8.divmod(3) => [2,2]

Front 62

What does #join(separator) do?

Back 62

Returns a string created by converting each element of the array to a string, separated by the given separator

Front 63

What does #split(pattern) do?

Back 63

Divides str into substrings based on a pattern, returning an array of these substrings. If pattern is a String, then its contents are used as the delimiter when splitting str. If pattern is a single space, str is split on whitespace, with leading whitespace and runs of contiguous whitespace characters ignored.

Front 64

What does .include? Do?

Back 64

check if array includes a value.

Front 65

What does #index do?

Back 65

arr.index(“simon”) => returns index of element in array

Front 66

what does #send do?

Back 66

send sends a message to an object instance and its ancestors in class hierarchy until some method reacts (because its name matches the first argument). Ex: 1.send('+') 2 => 3

Front 67

How do you check if every item, at least one or no item in a collection fulfills a certain criteria?

Back 67

collection.all?{|k,v| code } , any? and none?. Returns true or false.

Front 68

What does require do?

Back 68

Adds functionality from module, class or library to current code. Loads only once.

Front 69

What does load do?

Back 69

Same thing as require but is loaded in every time load is called.

Front 70

What's the difference between an Integer and a Float?

Back 70

Numbers after the comma. Dot notation converts integers into floats. 1.0 + 2 = 3.0.

Front 71

What's the difference between =, ==, and ===?

Back 71

Assignment, comparison and comparison with type.

Front 72

How do you do exponents in Ruby?

Back 72

3**2

Front 73

What is a range?

Back 73

an interval between two values

Front 74

How do you create a range (2 ways)? And what is the difference between .. and ...

Back 74

[1..10].to_a includes 10, [1...10].to_a excludes 10, [“a”..”z”].to_a, 1.upto(10), 10.downto(1).to_a

Front 75

What is string interpolation?

Back 75

Evaluating a variable inside a string #{variables}

Front 76

What are escape characters?

Back 76

(newline), \t (horizontal tab)

Front 77

How do you concatenate strings?

Back 77

“simon” + “ is cool” or “simon” << “ is cool”

Front 78

How are strings and arrays similar?

Back 78

They are both objects and can be accessed like string[0..3]

Front 79

What is a symbol?

Back 79

A pointer which is used as a record locator for a value/object. This saves memory since it’s only created once and stays the same. Mystring = :symbol

Front 80

What is a Regular Expression (RegEx). How do I select (all) numbers, characters, certain types, do exclusions, use ranges of letters/numbers, one character multiple times, several characters multiple times with range?

Back 80

a sequence of symbols and characters expressing a string or pattern to be searched for within a longer piece of text. "test123"[/\d+/] => 123.

Front 81

What are three ways to create an array?

Back 81

arr = Array.new(0), arr = [], arr = %w(1 2 3)

Front 82

How do you combine arrays (3 ways)?

Back 82

array1 + array2, array1.push(array2), array1 << array2

Front 83

How do you find the values in one array that aren't in another?

Back 83

array1 - array2

Front 84

How do you find values in both arrays?

Back 84

Use the intersection operator &. x = [1, 2, 4] y = [5, 2, 4] x & y # => [2, 4]

Front 85

What is the difference between push/pop and shift/unshift?

Back 85

Push/pop adds/removes to back and shift/unshift removes/adds to front.

Front 86

How is pushing or shoveling another array into your array different from just adding them together?

Back 86

The shovel only accepts 1 element.

Front 87

How do you delete items in an array (two methods)?

Back 87

arr.delete(8) or arr - [8]

Front 88

How do you find the biggest/smallest item in an array?

Back 88

arr.minmax

Front 89

How do you remove any duplicates from your array?

Back 89

arr.uniq!

Front 90

How do you find out how big an array is?

Back 90

.length / .size / .count

Front 91

How do you put an array in order?

Back 91

.sort!

Front 92

What is a hash?

Back 92

A Hash is a collection of key-value pairs like this: "employee" => "salary". It is similar to an Array, except that indexing is done via arbitrary keys of any object type, not an integer index. hash[“employee”] => “salary”

Front 93

What are keys and values?

Back 93

keys are the pointers which point to the values in the hash.

Front 94

How is a hash similar to an Array?

Back 94

It’s also a collection of different object types

Front 95

How is a hash different from an Array?

Back 95

indexing is done via arbitrary keys of any object type, not an integer index.

Front 96

What are 2 ways to create a hash?

Back 96

hash = Hash.new, hash = {}

Front 97

What is the hash rocket?

Back 97

The equals and greater than sign which connects the key to the value.

Front 98

How do you access data in a hash?

Back 98

hash[“employee”] => “salary”

Front 99

How do you change data in a hash?

Back 99

hash[“employee”] = “salary”

Front 100

What are options hashes, splat arguments and double splat arguments?

Back 100

Options hashes are used a lot when need to pass optional arguments to method. function(arg, options={}), these can also be writtes as function(arg, **options) and passed in as function(1, a: “this”, b: “second”}. function(arg, *other) returns an array of other arguments.

Front 101

How do you delete data from a hash?

Back 101

hash.delete(key)

Front 102

How do you add hashes together?

Back 102

hash.merge(secondhash)

Front 103

How do you list out all the keys or values?

Back 103

hash.keys OR hash.values

Front 104

How do you see if the hash contains a key or value?

Back 104

hash.has_value?(value_you_seek) OR hash.key(key)

Front 105

How do you get the current date and time, Year? Month? Hour? Second? Weekday?

Back 105

require “time” and type Time.now (.second, .hour, .year, .month)

Front 106

How do you create a Time specifically for 12/25/2013?

Back 106

Time.mktime( year, month, day, hour, min, sec, usec )

Front 107

How do you find how many days have passed between two Time's?

Back 107

Time1 - Time2

Front 108

How would you find out the time that was 100 seconds ago? 10 days ago?

Back 108

Time.now – 60*60*24*10 (s*m*h*days)

Front 109

How do you check if something is nil?

Back 109

.nil?

Front 110

What's the difference between nil and blank and empty?

Back 110

Only nil is nil, empty? is a standard Ruby method on some objects like Arrays, Hashes and Strings. Its exact behaviour will depend on the specific object, but typically it returns true if the object contains no elements. Blank is rails only method

Front 111

What's the difference between puts and p and print?

Back 111

print executes to_s on object, puts does the same but adds newline and p calls inspect instead of to_s but also includes newline

Front 112

What do +=, -=, *= and /= do?

Back 112

return variable after calculation is done.

Front 113

What is parallel assignment?

Back 113

Multiple assignment. A,b = 1, 2 or a, b, c, d = 1

Front 114

What's the easiest way to swap two variables?

Back 114

x,y = y, x

Front 115

What’s a linked list?

Back 115

A linked list is a linear data structure where each node has a value and pointer to the next node. The last node point to nil.

Front 116

What are trees? (tree, binary tree, binary search tree, red-black tree)

Back 116

a group of data items and turn them into a tree full of nodes where each left node is "lower" than each right node. The tree starts with the "root node" and any node with no children is called a "leaf node".