From 0d5f0da80319688c82e57c4b644aeff9c9b13ddb Mon Sep 17 00:00:00 2001
From: fartem <jaman.smlnsk@gmail.com>
Date: Thu, 2 Jan 2025 11:55:27 +0300
Subject: [PATCH] 2025-01-02 v. 7.6.4: added "23. Merge k Sorted Lists"

---
 README.md                                 |  1 +
 leetcode-ruby.gemspec                     |  2 +-
 lib/hard/23_merge_k_sorted_lists.rb       | 35 +++++++++++++++
 test/hard/test_23_merge_k_sorted_lists.rb | 53 +++++++++++++++++++++++
 4 files changed, 90 insertions(+), 1 deletion(-)
 create mode 100644 lib/hard/23_merge_k_sorted_lists.rb
 create mode 100644 test/hard/test_23_merge_k_sorted_lists.rb

diff --git a/README.md b/README.md
index 1745fdfb..3e683c41 100644
--- a/README.md
+++ b/README.md
@@ -633,3 +633,4 @@ 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)        |
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index 9271b041..884b8759 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 = '7.6.3'
+  s.version = '7.6.4'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/hard/23_merge_k_sorted_lists.rb b/lib/hard/23_merge_k_sorted_lists.rb
new file mode 100644
index 00000000..09e976a2
--- /dev/null
+++ b/lib/hard/23_merge_k_sorted_lists.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require_relative '../common/linked_list'
+
+# https://leetcode.com/problems/merge-k-sorted-lists/
+# @param {ListNode[]} lists
+# @return {ListNode}
+def merge_k_lists(lists)
+  return if lists.size.zero?
+
+  new_head = ::ListNode.new(0, lists[0])
+  (1...lists.size).each do |i|
+    a = new_head.next
+    b = lists[i]
+    prev = new_head
+
+    while a && b
+      if a.val >= b.val
+        prev.next = ::ListNode.new(b.val)
+        prev.next.next = a
+        b = b.next
+        a = prev.next
+
+        next
+      end
+
+      prev = a
+      a = a.next
+    end
+
+    prev.next = b if b
+  end
+
+  new_head.next
+end
diff --git a/test/hard/test_23_merge_k_sorted_lists.rb b/test/hard/test_23_merge_k_sorted_lists.rb
new file mode 100644
index 00000000..c7ac9bfc
--- /dev/null
+++ b/test/hard/test_23_merge_k_sorted_lists.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/common/linked_list'
+require_relative '../../lib/hard/23_merge_k_sorted_lists'
+require 'minitest/autorun'
+
+class MergeKSortedListsTest < ::Minitest::Test
+  def test_default_one
+    assert(
+      ::ListNode.are_equals(
+        ::ListNode.from_array(
+          [1, 1, 2, 3, 4, 4, 5, 6]
+        ),
+        merge_k_lists(
+          [
+            ::ListNode.from_array(
+              [1, 4, 5]
+            ),
+            ::ListNode.from_array(
+              [1, 3, 4]
+            ),
+            ::ListNode.from_array(
+              [2, 6]
+            )
+          ]
+        )
+      )
+    )
+  end
+
+  def test_default_two
+    assert(
+      ::ListNode.are_equals(
+        ::ListNode.from_array([]),
+        merge_k_lists([])
+      )
+    )
+  end
+
+  def test_default_three
+    assert(
+      ::ListNode.are_equals(
+        ::ListNode.from_array([]),
+        merge_k_lists(
+          [
+            ::ListNode.from_array([])
+          ]
+        )
+      )
+    )
+  end
+end