2024-08-09 v. 6.4.3: added "114. Flatten Binary Tree to Linked List"

README.md

@@ -508,3 +508,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 107. Binary Tree Level Order Traversal II                       | [Link](https://leetcode.com/problems/binary-tree-level-order-traversal-ii/)                       | [Link](./lib/medium/107_binary_tree_level_order_traversal_ii.rb)                       |
 | 109. Convert Sorted List to Binary Search Tree                  | [Link](https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/)                  | [Link](./lib/medium/109_convert_sorted_list_to_binary_search_tree.rb)                  |
 | 113. Path Sum II                                                | [Link](https://leetcode.com/problems/path-sum-ii/)                                                | [Link](./lib/medium/113_path_sum_ii.rb)                                                |
+| 114. Flatten Binary Tree to Linked List                         | [Link](https://leetcode.com/problems/flatten-binary-tree-to-linked-list/)                         | [Link](./lib/medium/114_flatten_binary_tree_to_linked_list.rb)                         |

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 = '6.4.2.1'
+  s.version = '6.4.3'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'

lib/medium/114_flatten_binary_tree_to_linked_list.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/flatten-binary-tree-to-linked-list/
+# @param {TreeNode} root
+# @return {Void} Do not return anything, modify root in-place instead.
+def flatten(root)
+  return unless root
+
+  return if root.left.nil? && root.right.nil?
+
+  unless root.left.nil?
+    flatten(root.left)
+
+    temp = root.right
+    root.right = root.left
+    root.left = nil
+
+    tail = root.right
+    tail = tail.right until tail.right.nil?
+
+    tail.right = temp
+  end
+
+  flatten(root.right)
+end

test/medium/test_114_flatten_binary_tree_to_linked_list.rb

@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/common/binary_tree'
+require_relative '../../lib/medium/114_flatten_binary_tree_to_linked_list'
+require 'minitest/autorun'
+
+class FlattenBinaryTreeToLinkedListTest < ::Minitest::Test
+  def test_default
+    input = ::TreeNode.new(
+      1,
+      ::TreeNode.new(
+        2,
+        ::TreeNode.new(3),
+        ::TreeNode.new(4)
+      ),
+      ::TreeNode.new(
+        5,
+        ::TreeNode.new(6),
+        nil
+      )
+    )
+    flatten(input)
+
+    assert(
+      ::TreeNode.are_equals(
+        ::TreeNode.new(
+          1,
+          nil,
+          ::TreeNode.new(
+            2,
+            nil,
+            ::TreeNode.new(
+              3,
+              nil,
+              ::TreeNode.new(
+                4,
+                nil,
+                ::TreeNode.new(
+                  5,
+                  nil,
+                  ::TreeNode.new(6)
+                )
+              )
+            )
+          )
+        ),
+        input
+      )
+    )
+
+    input = nil
+    flatten(input)
+
+    assert_nil(input)
+
+    input = ::TreeNode.new(0)
+    flatten(input)
+
+    assert(
+      ::TreeNode.are_equals(
+        ::TreeNode.new(0),
+        input
+      )
+    )
+  end
+end