AlexVPopov

#!/usr/bin/env bash

uninstall() {
  list=`gem list --no-versions`
  for gem in $list; do
    gem uninstall $gem -aIx
  done
  gem list
  gem install bundler
}

AlexVPopov

Let's say you have the following models:

class Admin < ActiveRecord::Base
  has_one :login, as: :loginable
end

class User < ActiveRecord::Base
  has_one :login, as: :loginable
end

AlexVPopov

def FindLargestPrime(n)
  return 1 if n == 1
  prime_factor = 2
  while prime_factor * prime_factor <= n do
    if n % prime_factor == 0 then n /= prime_factor
    else prime_factor += 1
    end
  end
  n
end

AlexVPopov

fib1 = 1
fib2 = 2
sum = fib2
fib = 0

until (fib >= 4000000)
  fib = fib1 + fib2
  fib1 = fib2
  fib2 = fib
  sum += fib if fib.even?

AlexVPopov

Project Euler 1sum = 0

(1...1000).each do |num|
  sum += num if num % 3 == 0 || num % 5 == 0
end

puts sum

AlexVPopov

def palindrome?(a)
  a.to_s == a.to_s.reverse
end

def dev_by_3digit?(a)
  999.downto(100) do |i|
    if a % i == 0 && a / i < 999
      return true
    end
  end

AlexVPopov

def devisible?(num, limit)
  devisible = true
	limit.downto(1) do |i|
		devisible = false if num % i != 0
		break if !devisible
	end
	devisible
end

def smallest_multiple(limit)

AlexVPopov

def sum_of_squares(num)
  (1..num).inject { |mem, var| mem + var ** 2  }
end

def square_of_sum(num)
	sum = (1..num).inject { |mem, var| mem + var  }
	sum ** 2
end

p square_of_sum(100) - sum_of_squares(100)

AlexVPopov

# Sum of first n numbers is n(n+1)/2
# Sum of squares of first n numbers is n(n+1)(2n + 1)/6
# Expanded form for sum ^ 2 - sum of squares = n^4/4+n^3/6-n^2/4-n/6

def formula(n)
  (n ** 4) / 4 + (n ** 3) / 6 - (n ** 2) / 4 - n / 6
end

p formula(100)

AlexVPopov

require 'prime'
primes = Prime.first 10001
p primes.last