2024-11-08 v. 6.9.9: added "400. Nth Digit"

Author: fartem

README.md

@@ -564,3 +564,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 388. Longest Absolute File Path                                 | [Link](https://leetcode.com/problems/longest-absolute-file-path/)                                 | [Link](./lib/medium/388_longest_absolute_file_path.rb)                                 | [Link](./test/medium/test_388_longest_absolute_file_path.rb)                                 |
 | 394. Decode String                                              | [Link](https://leetcode.com/problems/decode-string/)                                              | [Link](./lib/medium/394_decode_string.rb)                                              | [Link](./test/medium/test_394_decode_string.rb)                                              |
 | 398. Random Pick Index                                          | [Link](https://leetcode.com/problems/random-pick-index/)                                          | [Link](./lib/medium/398_random_pick_index.rb)                                          | [Link](./test/medium/test_398_random_pick_index.rb)                                          |
+| 400. Nth Digit                                                  | [Link](https://leetcode.com/problems/nth-digit/)                                                  | [Link](./lib/medium/400_nth_digit.rb)                                                  | [Link](./test/medium/test_400_nth_digit.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 = '6.9.8.1'
+  s.version = '6.9.9'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'

lib/medium/400_nth_digit.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/nth-digit/
+# @param {Integer} n
+# @return {Integer}
+def find_nth_digit(n)
+  sz = 1
+  p = 1
+
+  loop do
+    d = 9 * sz * p
+
+    return ((n - 1) / sz + p).to_s[(n - 1) % sz].to_i if n <= d
+
+    n -= d
+    sz += 1
+    p *= 10
+  end
+end

test/medium/test_400_nth_digit.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/medium/400_nth_digit'
+require 'minitest/autorun'
+
+class NthDigitTest < ::Minitest::Test
+  def test_default_one = assert_equal(3, find_nth_digit(3))
+
+  def test_default_two = assert_equal(0, find_nth_digit(11))
+end