From 45031c8ef84061f34e98241f750474c7d505a837 Mon Sep 17 00:00:00 2001
From: fartem <jaman.smlnsk@gmail.com>
Date: Fri, 11 Oct 2024 09:02:19 +0300
Subject: [PATCH] 2024-10-11 v. 6.8.0: added "287. Find the Duplicate Number"

---
 README.md                                     |  1 +
 leetcode-ruby.gemspec                         |  2 +-
 lib/medium/287_find_the_duplicate_number.rb   | 25 +++++++++++++++++++
 .../test_287_find_the_duplicate_number.rb     | 13 ++++++++++
 4 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 lib/medium/287_find_the_duplicate_number.rb
 create mode 100644 test/medium/test_287_find_the_duplicate_number.rb

diff --git a/README.md b/README.md
index d79eea09..a5136f65 100644
--- a/README.md
+++ b/README.md
@@ -545,3 +545,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 238. Product of Array Except Self                               | [Link](https://leetcode.com/problems/product-of-array-except-self/)                               | [Link](./lib/medium/238_product_of_array_except_self.rb)                               | [Link](./test/medium/test_238_product_of_array_except_self.rb)                               |
 | 240. Search a 2D Matrix II                                      | [Link](https://leetcode.com/problems/search-a-2d-matrix-ii/)                                      | [Link](./lib/medium/240_search_a_2d_matrix_ii.rb)                                      | [Link](./test/medium/test_240_search_a_2d_matrix_ii.rb)                                      |
 | 284. Peeking Iterator                                           | [Link](https://leetcode.com/problems/peeking-iterator/)                                           | [Link](./lib/medium/284_peeking_iterator.rb)                                           | [Link](./test/medium/test_284_peeking_iterator.rb)                                           |
+| 287. Find the Duplicate Number                                  | [Link](https://leetcode.com/problems/find-the-duplicate-number/)                                  | [Link](./lib/medium/287_find_the_duplicate_number.rb)                                  | [Link](./test/medium/test_287_find_the_duplicate_number.rb)                                  |
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index c8ae1f65..cf3d931c 100644
--- a/leetcode-ruby.gemspec
+++ b/leetcode-ruby.gemspec
@@ -5,7 +5,7 @@ require 'English'
 ::Gem::Specification.new do |s|
   s.required_ruby_version = '>= 3.0'
   s.name = 'leetcode-ruby'
-  s.version = '6.7.9'
+  s.version = '6.8.0'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/medium/287_find_the_duplicate_number.rb b/lib/medium/287_find_the_duplicate_number.rb
new file mode 100644
index 00000000..d5d22fea
--- /dev/null
+++ b/lib/medium/287_find_the_duplicate_number.rb
@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/find-the-duplicate-number/
+# @param {Integer[]} nums
+# @return {Integer}
+def find_duplicate(nums)
+  tortoise = nums.first
+  hare = nums.first
+
+  loop do
+    tortoise = nums[tortoise]
+    hare = nums[nums[hare]]
+
+    break if tortoise == hare
+  end
+
+  tortoise = nums.first
+
+  until tortoise == hare
+    tortoise = nums[tortoise]
+    hare = nums[hare]
+  end
+
+  hare
+end
diff --git a/test/medium/test_287_find_the_duplicate_number.rb b/test/medium/test_287_find_the_duplicate_number.rb
new file mode 100644
index 00000000..5fbd9909
--- /dev/null
+++ b/test/medium/test_287_find_the_duplicate_number.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/medium/287_find_the_duplicate_number'
+require 'minitest/autorun'
+
+class FindTheDuplicateNumberTest < ::Minitest::Test
+  def test_default_one = assert_equal(2, find_duplicate([1, 3, 4, 2, 2]))
+
+  def test_default_two = assert_equal(3, find_duplicate([3, 1, 3, 4, 2]))
+
+  def test_default_three = assert_equal(3, find_duplicate([3, 3, 3, 3, 3]))
+end