2025-01-08 v. 7.7.8: added "880. Decoded String at Index"

Author: fartem

README.md

@@ -632,6 +632,7 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 863. All Nodes Distance K in Binary Tree                        | [Link](https://leetcode.com/problems/all-nodes-distance-k-in-binary-tree/)                        | [Link](./lib/medium/863_all_nodes_distance_k_in_binary_tree.rb)                        | [Link](./test/medium/test_863_all_nodes_distance_k_in_binary_tree.rb)                        |
 | 865. Smallest Subtree with all the Deepest Nodes                | [Link](https://leetcode.com/problems/smallest-subtree-with-all-the-deepest-nodes/)                | [Link](./lib/medium/865_smallest_subtree_with_all_the_deepest_nodes.rb)                | [Link](./test/medium/test_865_smallest_subtree_with_all_the_deepest_nodes.rb)                |
 | 869. Reordered Power of 2                                       | [Link](https://leetcode.com/problems/reordered-power-of-2/)                                       | [Link](./lib/medium/869_reordered_power_of_2.rb)                                       | [Link](./test/medium/test_869_reordered_power_of_2.rb)                                       |
+| 880. Decoded String at Index                                    | [Link](https://leetcode.com/problems/decoded-string-at-index/)                                    | [Link](./lib/medium/880_decoded_string_at_index.rb)                                    | [Link](./test/medium/test_880_decoded_string_at_index.rb)                                    |
 
 ### Hard
 

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 = '7.7.7'
+  s.version = '7.7.8'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'

lib/medium/880_decoded_string_at_index.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/decoded-string-at-index/
+# @param {String} s
+# @param {Integer} k
+# @return {String}
+def decode_at_index(s, k)
+  size = 0
+
+  s.each_char do |c|
+    if c =~ /[0-9]/
+      size *= c.to_i
+    else
+      size += 1
+    end
+  end
+
+  s.each_char.reverse_each do |c|
+    k %= size
+
+    return c if k.zero? && c =~ /[A-Za-z]/
+
+    if c =~ /[0-9]/
+      size /= c.to_i
+    else
+      size -= 1
+    end
+  end
+end

test/medium/test_880_decoded_string_at_index.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/medium/880_decoded_string_at_index'
+require 'minitest/autorun'
+
+class DecodedStringAtIndexTest < ::Minitest::Test
+  def test_default_one
+    assert_equal(
+      'o',
+      decode_at_index(
+        'leet2code3',
+        10
+      )
+    )
+  end
+
+  def test_default_two
+    assert_equal(
+      'h',
+      decode_at_index(
+        'ha22',
+        5
+      )
+    )
+  end
+
+  def test_default_three
+    assert_equal(
+      'a',
+      decode_at_index(
+        'a2345678999999999999999',
+        1
+      )
+    )
+  end
+end