Aaron Feng

start = Time.now
sum_of_squares = 0
square_of_sums = 0

(1..100).each do |n|
  sum_of_squares = sum_of_squares + n ** 2  
  square_of_sums = square_of_sums + n  
end

puts "Took: #{Time.now - start} seconds"
puts (square_of_sums ** 2) - sum_of_squares

max = 150000
table = {}
prime = [] 

start = Time.now

(2..max).each do |n|
  table[n.to_s] = n
end

(2..(max + 1 / 2)).each do |n|
  unless table[n.to_s].nil? then prime << n; end
  if prime.length >= 10001 then break; end
  index = n + n 
  while index <= max
    table.delete(index.to_s)
    index = index + n
  end
end

puts "Took: #{Time.now - start} seconds"
puts "#{prime.length} prime is #{prime.last}"

lines = DATA.readlines

greatest = 0
greatest_5 = []

start = Time.now

lines.each do |line|
  line_chars = line.split(//)

  while not line_chars.empty?
    result = 1
    next_5 = line_chars.slice(0,5)

    next_5.each do |n|
      result = n.to_i * result
    end

    if result > greatest
      greatest = result
      greatest_5.replace(next_5)
    end

    line_chars.slice!(0,1)
  end

end

puts "Took: #{Time.now - start} seconds"
puts "#{greatest}"
__END__
73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450

start = Time.now
(1..1000).each do |a|
  ((a + 1)..1000).each do |b|
    a_2 = a ** 2
    b_2 = b ** 2
    c = Math.sqrt(a_2 + b_2)
    if c == c.to_i
      c = c.to_i
      c_2 = c ** 2

      sum =  Math.sqrt(a_2) + Math.sqrt(b_2) + Math.sqrt(c_2) 

      if sum == 1000 
        puts "Took: #{Time.now - start} seconds"
        p "#{a} + #{b} + #{c} = #{a + b + c}"
        p "Product is #{a * b * c}"
        exit
      end     
    end
  end
end

start = Time.now

max_prime = 2000000 
table = {}
(2...max_prime).each do |n|
  table[n.to_s] = n
end

(2...(max_prime / 2)).each do |n|
  index = n + n 

  while index < max_prime
    table.delete(index.to_s)
    index = index + n
  end
end

result = 0

table.each do |k,v|
  result = result + v
end

puts "Took: #{Time.now - start} seconds"
puts "Result is: #{result}"