From 55e16ab995caa8e8dc045f0362bd71d1fd2d7425 Mon Sep 17 00:00:00 2001
From: vzvu3k6k <vzvu3k6k@gmail.com>
Date: Thu, 29 Oct 2020 04:58:00 +0900
Subject: [PATCH 1/5] Add solution for the Project Euler Problem 4

---
 Project Euler/Problem 4/problem4_sol1.rb | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 Project Euler/Problem 4/problem4_sol1.rb

diff --git a/Project Euler/Problem 4/problem4_sol1.rb b/Project Euler/Problem 4/problem4_sol1.rb
new file mode 100644
index 0000000..b7e9d43
--- /dev/null
+++ b/Project Euler/Problem 4/problem4_sol1.rb	
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class Integer
+  def parindrome?
+    self == reverse
+  end
+
+  # 123.reverse == 321
+  # 100.reverse == 1
+  def reverse
+    result = 0
+    n = self
+    loop do
+      result = result * 10 + n % 10
+      break if (n /= 10).zero?
+    end
+    result
+  end
+end
+
+factors = (100..999).to_a
+products = factors.product(factors).map { _1 * _2 }
+puts products.select(&:parindrome?).max

From 459f674ec2726477162693caf7cc43ff249e9e25 Mon Sep 17 00:00:00 2001
From: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Date: Thu, 29 Oct 2020 18:53:01 +0000
Subject: [PATCH 2/5] updating DIRECTORY.md

---
 DIRECTORY.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index e828438..80e7163 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -26,6 +26,8 @@
     * [Problem2 Sol1](https://github.com/TheAlgorithms/Ruby/blob/master/Project%20Euler/Problem%202/problem2_sol1.rb)
   * Problem 3
     * [Problem3 Sol1](https://github.com/TheAlgorithms/Ruby/blob/master/Project%20Euler/Problem%203/problem3_sol1.rb)
+  * Problem 4
+    * [Problem4 Sol1](https://github.com/TheAlgorithms/Ruby/blob/master/Project%20Euler/Problem%204/problem4_sol1.rb)
   * Problem 5
     * [Problem5 Sol1](https://github.com/TheAlgorithms/Ruby/blob/master/Project%20Euler/Problem%205/problem5_sol1.rb)
 

From bcd82560aa938e5a7fd11f6c6bdf0e1236fb363a Mon Sep 17 00:00:00 2001
From: vzvu3k6k <vzvu3k6k@gmail.com>
Date: Thu, 31 Dec 2020 00:42:34 +0900
Subject: [PATCH 3/5] Rename solution file

---
 .../Problem 4/problem4_sol1.rb => project_euler/problem_4/sol2.rb | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename Project Euler/Problem 4/problem4_sol1.rb => project_euler/problem_4/sol2.rb (100%)

diff --git a/Project Euler/Problem 4/problem4_sol1.rb b/project_euler/problem_4/sol2.rb
similarity index 100%
rename from Project Euler/Problem 4/problem4_sol1.rb
rename to project_euler/problem_4/sol2.rb

From 770fc9622c5a42ee5ee6d32cd0915361e73d3de5 Mon Sep 17 00:00:00 2001
From: vzvu3k6k <vzvu3k6k@gmail.com>
Date: Thu, 31 Dec 2020 00:44:04 +0900
Subject: [PATCH 4/5] Add problem description copying from sol1.rb

---
 project_euler/problem_4/sol2.rb | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/project_euler/problem_4/sol2.rb b/project_euler/problem_4/sol2.rb
index b7e9d43..fd881e2 100644
--- a/project_euler/problem_4/sol2.rb
+++ b/project_euler/problem_4/sol2.rb
@@ -1,5 +1,8 @@
 # frozen_string_literal: true
 
+# 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.
+
 class Integer
   def parindrome?
     self == reverse

From 3405abe9d35b8a3eb52a9b56daa840a929981995 Mon Sep 17 00:00:00 2001
From: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Date: Wed, 30 Dec 2020 15:46:16 +0000
Subject: [PATCH 5/5] updating DIRECTORY.md

---
 DIRECTORY.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 7e05b7e..6aaeca9 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -43,6 +43,7 @@
     * [Sol2](https://github.com/TheAlgorithms/Ruby/blob/master/project_euler/problem_3/sol2.rb)
   * Problem 4
     * [Sol1](https://github.com/TheAlgorithms/Ruby/blob/master/project_euler/problem_4/sol1.rb)
+    * [Sol2](https://github.com/TheAlgorithms/Ruby/blob/master/project_euler/problem_4/sol2.rb)
   * Problem 5
     * [Sol1](https://github.com/TheAlgorithms/Ruby/blob/master/project_euler/problem_5/sol1.rb)