Merge pull request #793 from fartem/516-Longest-Palindromic-Subsequence

2024-12-05 v. 7.2.2: added "516. Longest Palindromic Subsequence"

Author: fartem

README.md

@@ -587,3 +587,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 508. Most Frequent Subtree Sum                                  | [Link](https://leetcode.com/problems/most-frequent-subtree-sum/)                                  | [Link](./lib/medium/508_most_frequent_subtree_sum.rb)                                  | [Link](./test/medium/test_508_most_frequent_subtree_sum.rb)                                  |
 | 513. Find Bottom Left Tree Value                                | [Link](https://leetcode.com/problems/find-bottom-left-tree-value/)                                | [Link](./lib/medium/513_find_bottom_left_tree_value.rb)                                | [Link](./test/medium/test_513_find_bottom_left_tree_value.rb)                                |
 | 515. Find Largest Value in Each Tree Row                        | [Link](https://leetcode.com/problems/find-largest-value-in-each-tree-row/)                        | [Link](./lib/medium/515_find_largest_value_in_each_tree_row.rb)                        | [Link](./test/medium/test_515_find_largest_value_in_each_tree_row.rb)                        |
+| 516. Longest Palindromic Subsequence                            | [Link](https://leetcode.com/problems/longest-palindromic-subsequence/)                            | [Link](./lib/medium/516_longest_palindromic_subsequence.rb)                            | [Link](./test/medium/test_516_longest_palindromic_subsequence.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 = '7.2.1'
+  s.version = '7.2.2'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'

lib/medium/516_longest_palindromic_subsequence.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/longest-palindromic-subsequence/
+# @param {String} s
+# @return {Integer}
+def longest_palindrome_subseq(s) = calculate_length(s, 0, s.size - 1, {})
+
+private
+
+# @param {String} s
+# @param {Integer} st
+# @param {Integer} nd
+# @param {Map<Integer, Integer>} subs
+# @return {Integer}
+def calculate_length(s, st, nd, subs)
+  return 0 if st > nd
+
+  return 1 if st == nd
+
+  s_ch = s[st]
+  e_ch = s[nd]
+  key = "#{st}/#{nd}"
+  unless subs.include?(key)
+    curr_length =
+      if s_ch == e_ch
+        calculate_length(s, st + 1, nd - 1, subs) + 2
+      else
+        [
+          calculate_length(s, st + 1, nd, subs),
+          calculate_length(s, st, nd - 1, subs)
+        ].max
+      end
+
+    subs[key] = curr_length
+  end
+
+  subs[key]
+end

test/medium/test_516_longest_palindromic_subsequence.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/medium/516_longest_palindromic_subsequence'
+require 'minitest/autorun'
+
+class LongestPalindromicSubsequenceTest < ::Minitest::Test
+  def test_default_one
+    assert_equal(
+      4,
+      longest_palindrome_subseq(
+        'bbbab'
+      )
+    )
+  end
+
+  def test_default_two
+    assert_equal(
+      2,
+      longest_palindrome_subseq(
+        'cbbd'
+      )
+    )
+  end
+end