Merge pull request #653 from fartem/5_Longest_Palindromic_Substring

2024-06-25 v. 5.9.6: added "5. Longest Palindromic Substring"

Author: fartem

README.md

@@ -461,3 +461,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 |---------------------------------------------------|---------------------------------------------------------------------------------------|--------------------------------------------------------------------------|
 | 2. Add Two Numbers                                | [Link](https://leetcode.com/problems/add-two-numbers/)                                | [Link](./lib/medium/2_add_two_numbers.rb)                                |
 | 3. Longest Substring Without Repeating Characters | [Link](https://leetcode.com/problems/longest-substring-without-repeating-characters/) | [Link](./lib/medium/3_longest_substring_without_repeating_characters.rb) |
+| 5. Longest Palindromic Substring                  | [Link](https://leetcode.com/problems/longest-palindromic-substring/)                  | [Link](./lib/medium/5_longest_palindromic_substring.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 = '5.9.5'
+  s.version = '5.9.6'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[bin/leetcode-ruby README.md LICENSE]
   s.executable = 'leetcode-ruby'

lib/medium/5_longest_palindromic_substring.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/longest-palindromic-substring/
+# @param {String} s
+# @return {String}
+def longest_palindrome5(s)
+  result = ''
+
+  (0...s.length).each do |i|
+    str1 = find_longest_palindrome(i, i, s)
+    str2 = find_longest_palindrome(i, i + 1, s)
+
+    result = [result, str1, str2].max_by(&:size)
+  end
+
+  result
+end
+
+# @param {Integer} l
+# @param {Integer} r
+# @param {String} s
+# @return {String}
+def find_longest_palindrome(l, r, s)
+  while l >= 0 && r < s.size && s[l] == s[r]
+    l -= 1
+    r += 1
+  end
+
+  s[(l + 1)..(r - 1)]
+end

test/medium/test_5_longest_palindromic_substring.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/medium/5_longest_palindromic_substring'
+require 'minitest/autorun'
+
+class LongestPalindromicSubstringTest < ::Minitest::Test
+  def test_default
+    assert_equal('bab', longest_palindrome5('babad'))
+    assert_equal('bb', longest_palindrome5('cbbd'))
+  end
+end