2024-10-18 v. 6.8.4: added "316. Remove Duplicate Letters"

README.md

@@ -549,3 +549,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 299. Bulls and Cows                                             | [Link](https://leetcode.com/problems/bulls-and-cows/)                                             | [Link](./lib/medium/299_bulls_and_cows.rb)                                             | [Link](./test/medium/test_299_bulls_and_cows.rb)                                             |
 | 300. Longest Increasing Subsequence                             | [Link](https://leetcode.com/problems/longest-increasing-subsequence/)                             | [Link](./lib/medium/300_longest_increasing_subsequence.rb)                             | [Link](./test/medium/test_300_longest_increasing_subsequence.rb)                             |
 | 304. Range Sum Query 2D - Immutable                             | [Link](https://leetcode.com/problems/range-sum-query-2d-immutable/)                               | [Link](./lib/medium/304_range_sum_query_2d_immutable.rb)                               | [Link](./test/medium/test_304_range_sum_query_2d_immutable.rb)                               |
+| 316. Remove Duplicate Letters                                   | [Link](https://leetcode.com/problems/remove-duplicate-letters/)                                   | [Link](./lib/medium/316_remove_duplicate_letters.rb)                                   | [Link](./test/medium/test_316_remove_duplicate_letters.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 = '6.8.3'
+  s.version = '6.8.4'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'

lib/medium/316_remove_duplicate_letters.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/remove-duplicate-letters/
+# @param {String} s
+# @return {String}
+def remove_duplicate_letters(s)
+  last_indices = ::Array.new(26, 0)
+  s.each_char.with_index { |c, i| last_indices[c.ord - 'a'.ord] = i }
+
+  seen = ::Array.new(26, false)
+  stack = []
+
+  s.each_char.with_index do |c, i|
+    c_index = c.ord - 'a'.ord
+
+    next if seen[c_index]
+
+    seen[stack.pop] = false while !stack.empty? && stack.last > c_index && i < last_indices[stack.last]
+
+    stack.push(c_index)
+    seen[c_index] = true
+  end
+
+  result = ''
+  result += (stack.pop + 'a'.ord).chr until stack.empty?
+
+  result.reverse
+end

test/medium/test_316_remove_duplicate_letters.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/medium/316_remove_duplicate_letters'
+require 'minitest/autorun'
+
+class RemoveDuplicateLettersTest < ::Minitest::Test
+  def test_default_one
+    assert_equal(
+      'abc',
+      remove_duplicate_letters(
+        'bcabc'
+      )
+    )
+  end
+
+  def test_default_two
+    assert_equal(
+      'acdb',
+      remove_duplicate_letters(
+        'cbacdcbc'
+      )
+    )
+  end
+end