Today I Learned - Week 2 Bootcamp

prime.rb

#Copyright Daniel Mai 04/30/2017
#Advanced Ruby coding: 
#Write me a function to generate/print/store the first “n” prime numbers.
#The algorithm to find prime numbers in inspired by the pseudocode provided in
#https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
#The sieve of Eratosthenes is quite efficient to quickly look up prime numbers
#in a list of n numbers


#Accept an input of up to 30 numbers
n = 30
#Create an array of Boolean values
#The array needs to have n-1 elements because the index at n would be n + 1
ary = Array.new(n - 1).map{ |value| value = true}


#0 and 1 are not prime numbers, so we don't need values
#at index 0 and index 1 in the array
ary.unshift(nil)
ary.unshift(nil)

#start the first iterator from 2
i = 2
#initialize an inner iterator
j = 0

#The idea is to eliminate all multiplications of i by setting their values to false
#For example, any multiplication of 2 is 4,6,8,10. Those are not prime numbers.

#Loop until i reaches the square root of input
while i <= Math.sqrt(n)
  #check if a number has any multiplication of itself
  if ary[i]
    #reset j iterator and initialize k
    k = 2
    j = 2
    #Perform the prime check
    while j <= n 
      #Set all multiplications of i to boolean value FALSE
      j = i * k
      #the if condition is to make sure j will not go higher than n
      ary[j] = false if j <= n
      
      #increment k
      k += 1
    end
  end
  #increment i
  i += 1
end

#Create an empty array to hold prime numbers
prime_numbers = []
#Loop through the array again
#Any value that is true, its index is a prime
ary.each_index do |value|
  if ary[value]
    prime_numbers << value
  end
end

#Output the result
p prime_numbers
#[2, 3, 5, 7, 11, 13, 17, 19, 23, 29]

TIL_week2.txt

------ Day 1 -------

create database on Rails:
rails db:create

rails generate model Recipe title:string chef:string ingredients:string directions:string image:string prep_time:integer

CRUD:
Read:
ModelName.all ==> return an array of hashes of all items in the database
ModelName.first / ModelName.last ==> return a hash of an item in the database
ModelName.where(attribute:"Name") => return all items that match the attribute
item.update(attribute:"New value") ==> update the item in the database
item.attribute = "new value"
item.save ==> save the change to the database
ModelName.create(attribute:"value") ==> create an item in the database

------ Day 2 -------
-------5/2/17----------

SASS: better than CSS?
SASS has things that CSS don't have:
- Variable
- Nesting

------ Day 3 -------

Three parts of an HTML request:

the verb (i.e GET)
the URL
the attribute
URL Parameters: Use wildcard (mywebsite.com/:wildcard) and query (mywebsite.com?querry=keyword) to navigate the website.
We can also use Form to submit information to the server

------ Day 4 -------

When using form to submit information, instead of just putting text next to the input textbox, wrap it in a <label> tag, for better web accessibility (for blinded people, the web browser will read what's inside the label tag, making them easier to understand the form).

------ Day 5 -------

People get hired just by blogging.

What to look for in a junior developer:

Enthusiam
Attention to detail
Hunger for learning
Thirst to contribute
What have you built?
How do you get unstuck?

Command+Shift+3: Take screen shot of whole screen
Command+Shift+4: Take screenshot of portion of the screen that you specify

When whiteboarding, always start with:
- The input
- Expected output