2025-01-09 v. 7.8.4: added "336. Palindrome Pairs"

Author: fartem

README.md

@@ -653,3 +653,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 233. Number of Digit One                      | [Link](https://leetcode.com/problems/number-of-digit-one/)                       | [Link](./lib/hard/233_number_of_digit_one.rb)                      | [Link](./test/hard/test_233_number_of_digit_one.rb)                      |
 | 239. Sliding Window Maximum                   | [Link](https://leetcode.com/problems/sliding-window-maximum/)                    | [Link](./lib/hard/239_sliding_window_maximum.rb)                   | [Link](./test/hard/test_239_sliding_window_maximum.rb)                   |
 | 297. Serialize and Deserialize Binary Tree    | [Link](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/)     | [Link](./lib/hard/297_serialize_and_deserialize_binary_tree.rb)    | [Link](./test/hard/test_297_serialize_and_deserialize_binary_tree.rb)    |
+| 336. Palindrome Pairs                         | [Link](https://leetcode.com/problems/palindrome-pairs/)                          | [Link](./lib/hard/336_palindrome_pairs.rb)                         | [Link](./test/hard/test_336_palindrome_pairs.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 = '7.8.3'
+  s.version = '7.8.4'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'

lib/hard/336_palindrome_pairs.rb

@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/palindrome-pairs/
+# @param {String[]} words
+# @return {Integer[][]}
+def palindrome_pairs(words)
+  result = []
+
+  word_map = words.each_with_index.to_h
+
+  words.each_with_index do |word, index|
+    valid_prefixes, valid_suffixes = get_partials(word)
+
+    valid_prefixes.each do |prefix|
+      reverse = prefix.reverse
+
+      next unless word_map[reverse] && index != word_map[reverse]
+
+      result << [index, word_map[reverse]]
+    end
+
+    valid_suffixes.each do |suffix|
+      reverse = suffix.reverse
+
+      result << [word_map[reverse], index] if word_map[reverse] && index != word_map[reverse]
+    end
+  end
+
+  result.uniq
+end
+
+private
+
+# @param {String} word
+# @return {Integer[]}
+def get_partials(word)
+  valid_prefixes = []
+  valid_suffixes = []
+
+  (0..word.length).each do |i|
+    prefix = word.slice(0, i)
+    suffix = word.slice(i, word.size)
+
+    valid_prefixes << prefix if suffix == suffix.reverse
+    valid_suffixes << suffix if prefix == prefix.reverse
+  end
+
+  [valid_prefixes, valid_suffixes]
+end

test/hard/test_336_palindrome_pairs.rb

@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/hard/336_palindrome_pairs'
+require 'minitest/autorun'
+
+class PalindromePairsTest < ::Minitest::Test
+  def test_default_one
+    assert_equal(
+      [
+        [0, 1],
+        [1, 0],
+        [3, 2],
+        [2, 4]
+      ],
+      palindrome_pairs(
+        %w[abcd dcba lls s sssll]
+      )
+    )
+  end
+
+  def test_default_two
+    assert_equal(
+      [
+        [0, 1],
+        [1, 0]
+      ],
+      palindrome_pairs(
+        %w[bat tab cat]
+      )
+    )
+  end
+
+  def test_default_three
+    assert_equal(
+      [
+        [0, 1],
+        [1, 0]
+      ],
+      palindrome_pairs(
+        ['a', '']
+      )
+    )
+  end
+end