PE probs

README.md

@@ -1,2 +1,4 @@
-DevPreWork01
+#DevPreWork01
 ============
+
+My prework for the [Startup Institute](www.startupinstitute.com).

pe1.rb

@@ -0,0 +1,8 @@
+total = 0
+(1...1000).each do |num|
+	if num%3 == 0 || num%5 == 0
+		total += num
+	end
+end
+
+puts total

pe10.rb

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+#THIS IS SLOW. ~5 MIN => Need to make more efficient
+
+require 'Prime'
+continue = true
+
+
+while continue
+	prime_array = Array.new
+	sum = 0
+
+	Prime.each(2_000_000) do |prime|
+		puts prime
+		sum += prime
+	end
+
+	puts sum
+
+	puts "Continue? "
+	go = gets.chomp
+	if go != 't'
+		continue = false
+	end
+end

pe2.rb

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+a = 0
+b = 1
+total = 0
+
+fibs = [1,2]
+
+while (fibs[a] + fibs[b]) < 4000000
+	fibs << (fibs[a] + fibs[b])
+	a += 1 
+	b += 1
+end
+
+fibs.each do |num|
+	if num%2 == 0 
+		total += num
+	end
+end
+
+puts total

pe3.rb

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+require 'Prime'
+
+
+
+continue = true
+
+while continue
+	max_num = 600851475143
+	primefact_array = Array.new
+
+	Prime.each(Math.sqrt(max_num)) do |prime|
+		if max_num%prime == 0
+			primefact_array << prime
+		end
+	end
+
+	puts primefact_array.last
+
+	puts 'Continue?'
+	go = gets.chomp
+	if go != 't'
+		continue = false
+	end
+end
+
+

pe4.rb

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+start_num = 999
+end_num = 1
+product_array = Array.new
+continue = true
+
+while continue 
+	start_num.downto(end_num) do |num1|
+		start_num.downto(end_num) do |num2|
+			product = num1*num2
+			if product.to_s == product.to_s.reverse
+				product_array << (num1*num2)
+			end
+		end
+	end
+
+	puts product_array.max
+
+	puts "Continue?"
+	go = gets.chomp
+
+	if go != 't'
+		continue = false
+	end
+end

pe5.rb

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+continue = true
+
+while continue
+	puts (1..20).inject(:lcm)
+
+	puts "\nContinue?"
+	go = gets.chomp
+	if go != 't'
+		continue = false
+	end
+end
+
+

pe6.rb

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+def sum_square
+	total = 0
+	(1..100).each do |num|
+		square = num **2
+		total += square
+	end
+	return total
+end
+
+def square_sum
+	sum = 0
+	(1..100).each do |num|
+		sum += num
+	end
+	return sum **2 
+end
+
+difference = (square_sum)- (sum_square)
+
+puts difference

pe7.rb

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+require 'Prime'
+
+
+continue = true
+
+while continue
+	prime_array = Prime.first 10_001
+	puts prime_array.last
+	puts "Keep going? "
+	go = gets.chomp
+	if go != 't'
+		continue = false
+	end
+end
+
+

pe8.rb

@@ -0,0 +1,53 @@
+num = '73167176531330624919225119674426574742355349194934
+		96983520312774506326239578318016984801869478851843
+		85861560789112949495459501737958331952853208805511
+		12540698747158523863050715693290963295227443043557
+		66896648950445244523161731856403098711121722383113
+		62229893423380308135336276614282806444486645238749
+		30358907296290491560440772390713810515859307960866
+		70172427121883998797908792274921901699720888093776
+		65727333001053367881220235421809751254540594752243
+		52584907711670556013604839586446706324415722155397
+		53697817977846174064955149290862569321978468622482
+		83972241375657056057490261407972968652414535100474
+		82166370484403199890008895243450658541227588666881
+		16427171479924442928230863465674813919123162824586
+		17866458359124566529476545682848912883142607690042
+		24219022671055626321111109370544217506941658960408
+		07198403850962455444362981230987879927244284909188
+		84580156166097919133875499200524063689912560717606
+		05886116467109405077541002256983155200055935729725
+		71636269561882670428252483600823257530420752963450'
+
+
+place = 0
+digits = 5
+continue = true
+
+product_array = Array.new
+
+def product (n)
+	total_product = 1
+	n.each_char do |char|
+		char = char.to_i
+		total_product *= char
+	end
+	return total_product
+end
+
+
+while continue
+	while place <= 995
+		string = num[place, digits]
+		product = product(string)
+		product_array << product 
+		place += 1
+	end
+
+	puts product_array.max
+	puts "Continue? "
+	go = gets.chomp
+	if go != 't'
+		continue = false
+	end
+end

pe9.rb

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+## This algorithm uses an algebraic manipulation of Euclid's equations
+
+(2..30).each do |m| 
+  (1...m).each do |n|
+    a = (m**2 - n**2)
+    b = 2*m*n 
+    c = (m**2 + n**2)
+
+    puts a*b*c if a+b+c==1000
+  end
+end