From 6691c24d5eae64ce92d4221b6b939515aea20a19 Mon Sep 17 00:00:00 2001
From: fartem <jaman.smlnsk@gmail.com>
Date: Tue, 31 Dec 2024 12:15:26 +0300
Subject: [PATCH] 2024-12-31 v. 7.5.6: added "784. Letter Case Permutation"

---
 README.md                                     |  1 +
 leetcode-ruby.gemspec                         |  2 +-
 lib/medium/784_letter_case_permutation.rb     | 34 +++++++++++++++++++
 .../test_784_letter_case_permutation.rb       | 25 ++++++++++++++
 4 files changed, 61 insertions(+), 1 deletion(-)
 create mode 100644 lib/medium/784_letter_case_permutation.rb
 create mode 100644 test/medium/test_784_letter_case_permutation.rb

diff --git a/README.md b/README.md
index eaea1b3a..381609d0 100644
--- a/README.md
+++ b/README.md
@@ -620,3 +620,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 735. Asteroid Collision                                         | [Link](https://leetcode.com/problems/asteroid-collision/)                                         | [Link](./lib/medium/735_asteroid_collision.rb)                                         | [Link](./test/medium/test_735_asteroid_collision.rb)                                         |
 | 739. Daily Temperatures                                         | [Link](https://leetcode.com/problems/daily-temperatures/)                                         | [Link](./lib/medium/739_daily_temperatures.rb)                                         | [Link](./test/medium/test_739_daily_temperatures.rb)                                         |
 | 763. Partition Labels                                           | [Link](https://leetcode.com/problems/partition-labels/)                                           | [Link](./lib/medium/763_partition_labels.rb)                                           | [Link](./test/medium/test_763_partition_labels.rb)                                           |
+| 784. Letter Case Permutation                                    | [Link](https://leetcode.com/problems/letter-case-permutation/)                                    | [Link](./lib/medium/784_letter_case_permutation.rb)                                    | [Link](./test/medium/test_784_letter_case_permutation.rb)                                    |
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index 2132fdb1..34e949c3 100644
--- a/leetcode-ruby.gemspec
+++ b/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 = '7.5.5'
+  s.version = '7.5.6'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/medium/784_letter_case_permutation.rb b/lib/medium/784_letter_case_permutation.rb
new file mode 100644
index 00000000..a561fce9
--- /dev/null
+++ b/lib/medium/784_letter_case_permutation.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/letter-case-permutation/
+
+# @param {String} s
+# @return {String[]}
+def letter_case_permutation(s)
+  result = []
+  find_permutations(s.chars, 0, result)
+
+  result
+end
+
+private
+
+# @param {Character[]} arr
+# @param {Integer} index
+# @param {String[]} result
+def find_permutations(arr, index, result)
+  if index == arr.size
+    result << arr.join
+
+    return
+  end
+
+  if arr[index] =~ /[A-Za-z]/
+    arr[index] = arr[index].downcase
+    find_permutations(arr, index + 1, result)
+
+    arr[index] = arr[index].upcase
+  end
+
+  find_permutations(arr, index + 1, result)
+end
diff --git a/test/medium/test_784_letter_case_permutation.rb b/test/medium/test_784_letter_case_permutation.rb
new file mode 100644
index 00000000..97892e40
--- /dev/null
+++ b/test/medium/test_784_letter_case_permutation.rb
@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/medium/784_letter_case_permutation'
+require 'minitest/autorun'
+
+class LetterCasePermutationTest < ::Minitest::Test
+  def test_default_one
+    assert_equal(
+      %w[a1b2 a1B2 A1b2 A1B2],
+      letter_case_permutation(
+        'a1b2'
+      )
+    )
+  end
+
+  def test_default_two
+    assert_equal(
+      %w[3z4 3Z4],
+      letter_case_permutation(
+        '3z4'
+      )
+    )
+  end
+end