Add solution for the Project Euler Problem 3

Project Euler/Problem 3/problem3_sol1.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+# The prime factors of 13195 are 5, 7, 13 and 29.
+# What is the largest prime factor of the number 600851475143
+
+# find all factors of the given number
+def get_factors(number)
+  factors = []
+  (1..Math.sqrt(number).to_i).each do |num|
+    if (number % num).zero?
+      factors << num
+      factors << number / num
+    end
+  end
+  factors
+end
+
+# determine if a given number is a prime number
+def prime?(number)
+  get_factors(number).length == 2
+end
+
+# find the largest prime
+def largest_prime_factor(number)
+  prime_factors = get_factors(number).select { |factor| prime?(factor) }
+  prime_factors.max
+end
+
+puts largest_prime_factor(600851475143)