From 91fbf85c9878e55cf6462092000b5d6eb6f28bd2 Mon Sep 17 00:00:00 2001
From: fartem <jaman.smlnsk@gmail.com>
Date: Thu, 2 Jan 2025 12:09:55 +0300
Subject: [PATCH] 2025-01-02 v. 7.6.5: added "25. Reverse Nodes in k-Group"

---
 README.md                                     |  1 +
 leetcode-ruby.gemspec                         |  2 +-
 lib/hard/25_reverse_nodes_in_k_group.rb       | 45 +++++++++++++++++++
 test/hard/test_25_reverse_nodes_in_k_group.rb | 40 +++++++++++++++++
 4 files changed, 87 insertions(+), 1 deletion(-)
 create mode 100644 lib/hard/25_reverse_nodes_in_k_group.rb
 create mode 100644 test/hard/test_25_reverse_nodes_in_k_group.rb

diff --git a/README.md b/README.md
index 3e683c41..752de644 100644
--- a/README.md
+++ b/README.md
@@ -634,3 +634,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 4. Median of Two Sorted Arrays  | [Link](https://leetcode.com/problems/median-of-two-sorted-arrays/) | [Link](./lib/hard/4_median_of_two_sorted_arrays.rb)  | [Link](./test/hard/test_4_median_of_two_sorted_arrays.rb)  |
 | 10. Regular Expression Matching | [Link](https://leetcode.com/problems/regular-expression-matching/) | [Link](./lib/hard/10_regular_expression_matching.rb) | [Link](./test/hard/test_10_regular_expression_matching.rb) |
 | 23. Merge k Sorted Lists        | [Link](https://leetcode.com/problems/merge-k-sorted-lists/)        | [Link](./lib/hard/23_merge_k_sorted_lists.rb)        | [Link](./test/hard/test_23_merge_k_sorted_lists.rb)        |
+| 25. Reverse Nodes in k-Group    | [Link](https://leetcode.com/problems/reverse-nodes-in-k-group/)    | [Link](./lib/hard/25_reverse_nodes_in_k_group.rb)    | [Link](./test/hard/test_25_reverse_nodes_in_k_group.rb)    |
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index 884b8759..3a72ce84 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 = '7.6.4'
+  s.version = '7.6.5'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/hard/25_reverse_nodes_in_k_group.rb b/lib/hard/25_reverse_nodes_in_k_group.rb
new file mode 100644
index 00000000..5444e5a7
--- /dev/null
+++ b/lib/hard/25_reverse_nodes_in_k_group.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/reverse-nodes-in-k-group/
+# @param {ListNode} head
+# @param {Integer} k
+# @return {ListNode}
+def reverse_k_group(head, k)
+  return unless head
+
+  return head unless has_next_for_reverse_k_group(head, k)
+
+  prev = nil
+  curr = head
+  nxt =  nil
+  count = 0
+
+  while curr && count < k
+    nxt = curr.next
+    curr.next = prev
+    prev = curr
+    curr = nxt
+
+    count += 1
+  end
+
+  head.next = reverse_k_group(nxt, k)
+
+  prev
+end
+
+private
+
+# @param {ListNode} head
+# @param {Integer} k
+# @return {Boolean}
+def has_next_for_reverse_k_group(head, k)
+  count = 0
+  p = head
+  while count != k && !p.nil?
+    p = p.next
+    count += 1
+  end
+
+  count == k
+end
diff --git a/test/hard/test_25_reverse_nodes_in_k_group.rb b/test/hard/test_25_reverse_nodes_in_k_group.rb
new file mode 100644
index 00000000..bb57fa8e
--- /dev/null
+++ b/test/hard/test_25_reverse_nodes_in_k_group.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/common/linked_list'
+require_relative '../../lib/hard/25_reverse_nodes_in_k_group'
+require 'minitest/autorun'
+
+class ReverseNodesInKGroupTest < ::Minitest::Test
+  def test_default_one
+    assert(
+      ::ListNode.are_equals(
+        ::ListNode.from_array(
+          [2, 1, 4, 3, 5]
+        ),
+        reverse_k_group(
+          ::ListNode.from_array(
+            [1, 2, 3, 4, 5]
+          ),
+          2
+        )
+      )
+    )
+  end
+
+  def test_default_two
+    assert(
+      ::ListNode.are_equals(
+        ::ListNode.from_array(
+          [3, 2, 1, 4, 5]
+        ),
+        reverse_k_group(
+          ::ListNode.from_array(
+            [1, 2, 3, 4, 5]
+          ),
+          3
+        )
+      )
+    )
+  end
+end