2025-01-06 v. 7.7.3: added "115. Distinct Subsequences"

Author: fartem

README.md

@@ -642,3 +642,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 30. Substring with Concatenation of All Words | [Link](https://leetcode.com/problems/substring-with-concatenation-of-all-words/) | [Link](./lib/hard/30_substring_with_concatenation_of_all_words.rb) | [Link](./test/hard/test_30_substring_with_concatenation_of_all_words.rb) |
 | 32. Longest Valid Parentheses                 | [Link](https://leetcode.com/problems/longest-valid-parentheses/)                 | [Link](./lib/hard/32_longest_valid_parentheses.rb)                 | [Link](./test/hard/test_32_longest_valid_parentheses.rb)                 |
 | 41. First Missing Positive                    | [Link](https://leetcode.com/problems/first-missing-positive/)                    | [Link](./lib/hard/41_first_missing_positive.rb)                    | [Link](./test/hard/test_41_first_missing_positive.rb)                    |
+| 115. Distinct Subsequences                    | [Link](https://leetcode.com/problems/distinct-subsequences/)                     | [Link](./lib/hard/115_distinct_subsequences.rb)                    | [Link](./test/hard/test_115_distinct_subsequences.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 = '7.7.2'
+  s.version = '7.7.3'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'

lib/hard/115_distinct_subsequences.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/distinct-subsequences/
+# @param {String} s
+# @param {String} t
+# @return {Integer}
+def num_distinct(s, t)
+  m = s.size
+  n = t.size
+  dp = ::Array.new(n + 1, 0)
+  dp[0] = 1
+
+  (1..m).each do |i|
+    (1..n).reverse_each do |j|
+      dp[j] = dp[j - 1] + dp[j] if s[i - 1] == t[j - 1]
+    end
+  end
+
+  dp[n]
+end

test/hard/test_115_distinct_subsequences.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/hard/115_distinct_subsequences'
+require 'minitest/autorun'
+
+class DistinctSubsequencesTest < ::Minitest::Test
+  def test_default_one
+    assert_equal(
+      3,
+      num_distinct(
+        'rabbbit',
+        'rabbit'
+      )
+    )
+  end
+
+  def test_default_two
+    assert_equal(
+      5,
+      num_distinct(
+        'babgbag',
+        'bag'
+      )
+    )
+  end
+end