Project Euler

README.md

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+
 DevPreWork01
 ============
+
+
+Problem #3
+ <p>The prime factors of 13195 are 5, 7, 13 and 29.
+
+What is the largest prime factor of the number 600851475143 ?</p>
+
+Problem #5 Smallest numebr
+<p>2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.
+
+What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20? </p> 
+
+Problem #8 largest product in a series
+
+<p> Find the greatest product of five consecutive digits in the 1000-digit number. </p>
+
+<p>73167176531330624919225119674426574742355349194934
+96983520312774506326239578318016984801869478851843
+85861560789112949495459501737958331952853208805511
+12540698747158523863050715693290963295227443043557
+66896648950445244523161731856403098711121722383113
+62229893423380308135336276614282806444486645238749
+30358907296290491560440772390713810515859307960866
+70172427121883998797908792274921901699720888093776
+65727333001053367881220235421809751254540594752243
+52584907711670556013604839586446706324415722155397
+53697817977846174064955149290862569321978468622482
+83972241375657056057490261407972968652414535100474
+82166370484403199890008895243450658541227588666881
+16427171479924442928230863465674813919123162824586
+17866458359124566529476545682848912883142607690042
+24219022671055626321111109370544217506941658960408
+07198403850962455444362981230987879927244284909188
+84580156166097919133875499200524063689912560717606
+05886116467109405077541002256983155200055935729725
+71636269561882670428252483600823257530420752963450</p>
+

problem01.rb

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+#if we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
+#Find the sum of all the multiples of 3 or 5 below 1000.
+
+counter = []
+
+(1..9).each do |x| 
+	counter <<  x if (x%3 == 0 || x%5==0) 
+	counter.inspect  
+end
+
+counter.inject { |sum, n| sum+n }
+#or 
+#counter.reduce(:+)

problem03.rb

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+
+
+
+#make method to check to see if number is prime
+
+def prime?(n)
+  (2..(n-1)).each { |x| return false if n % x == 0 }
+  true
+end
+
+n =63
+array = []
+limit = 1
+x = 2 
+
+#make loop that checks to see what the prime numbers and shovels them into an empty array
+while limit < n
+  if n % x == 0 && prime?(x) 
+    array << x
+    limit *= x
+  end
+  x += 1
+end
+
+#array of prime numbers
+array.inspect
+#grab the last number in array
+array.sort.last

problem04.rb

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+#A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 * 99.
+#Find the largest palindrome made from the product of two 3-digit numbers.
+
+#make a method to check if the number is a palindrome
+
+def palindrome?(n)
+	# convert n to a string
+	x = n.to_s
+	# get the length and divide by 2
+	y = x.length/2
+	# check to see if both sides equal
+	x[0..(y-1)] == x[-y..-1].reverse
+end
+
+
+def product_of_nums(n)
+  a = []
+  max_sum = 0
+
+  999.downto(100) do |i|
+    999.downto(100) do |j|
+      sum = i * j
+      if (sum > max_sum);
+        if (palindrome?(sum));
+          max_sum = sum
+          a << sum
+          break
+        end
+      end
+    end
+  end
+    return a.inspect;
+end
+
+puts "answer: #{product_of_nums(3)}"   
+
+

problem05.rb

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+#2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.
+#What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?
+
+# Ruby docs least common multiple lcm
+
+num=(1..20).to_a
+puts num.inject{ |x,n| x.lcm(n) }
+
+#find prime factors 
+def prime?(n)
+  (2..(n-1)).each {|x| return false if n % x == 0}
+  return true
+end