From 0aebe90a74755c9a83a511297002b29570930444 Mon Sep 17 00:00:00 2001
From: fartem <jaman.smlnsk@gmail.com>
Date: Thu, 11 Jul 2024 08:17:07 +0300
Subject: [PATCH] 2024-07-11 v. 6.1.2: added "39. Combination Sum"

---
 README.md                              |  1 +
 leetcode-ruby.gemspec                  |  2 +-
 lib/medium/39_combination_sum.rb       | 44 ++++++++++++++++++++++++++
 test/medium/test_39_combination_sum.rb | 13 ++++++++
 4 files changed, 59 insertions(+), 1 deletion(-)
 create mode 100644 lib/medium/39_combination_sum.rb
 create mode 100644 test/medium/test_39_combination_sum.rb

diff --git a/README.md b/README.md
index d129946a..7718f81b 100644
--- a/README.md
+++ b/README.md
@@ -477,3 +477,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 34. Find First and Last Position of Element in Sorted Array | [Link](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/) | [Link](./lib/medium/34_find_first_and_last_position_of_element_in_sorted_array.rb) |
 | 36. Valid Sudoku                                            | [Link](https://leetcode.com/problems/valid-sudoku/)                                            | [Link](./lib/medium/36_valid_sudoku.rb)                                            |
 | 38. Count and Say                                           | [Link](https://leetcode.com/problems/count-and-say/)                                           | [Link](./lib/medium/38_count_and_say.rb)                                           |
+| 39. Combination Sum                                         | [Link](https://leetcode.com/problems/combination-sum/)                                         | [Link](./lib/medium/39_combination_sum.rb)                                         |
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index 0ddc4e6c..2aa8b640 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 = '6.1.1'
+  s.version = '6.1.2'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[bin/leetcode-ruby README.md LICENSE]
   s.executable = 'leetcode-ruby'
diff --git a/lib/medium/39_combination_sum.rb b/lib/medium/39_combination_sum.rb
new file mode 100644
index 00000000..c27cd946
--- /dev/null
+++ b/lib/medium/39_combination_sum.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/combination-sum/
+# @param {Integer[]} candidates
+# @param {Integer} target
+# @return {Integer[][]}
+def combination_sum(candidates, target)
+  combine_sum(candidates, target, [], [])
+end
+
+private
+
+# @param {Integer[]} candidates
+# @param {Integer} target
+# @param {Integer[][]} result
+# @param {Integer[]} curr
+# @return {Integer[][]}
+def combine_sum(candidates, target, result, curr)
+  find_combination(candidates, target, 0, result, curr)
+
+  result
+end
+
+# @param {Integer[]} candidates
+# @param {Integer} target
+# @param {Integer} start
+# @param {Integer[][]} result
+# @param {Integer[]} curr
+# @return {Void}
+def find_combination(candidates, target, start, result, curr)
+  if target.zero?
+    result << curr.dup
+
+    return
+  end
+
+  return if target.negative?
+
+  (start...candidates.length).each do |i|
+    curr << candidates[i]
+    find_combination(candidates, target - candidates[i], i, result, curr)
+    curr.delete_at(curr.length - 1)
+  end
+end
diff --git a/test/medium/test_39_combination_sum.rb b/test/medium/test_39_combination_sum.rb
new file mode 100644
index 00000000..f415aadc
--- /dev/null
+++ b/test/medium/test_39_combination_sum.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/medium/39_combination_sum'
+require 'minitest/autorun'
+
+class CombinationSumTest < ::Minitest::Test
+  def test_default
+    assert_equal([[2, 2, 3], [7]], combination_sum([2, 3, 6, 7], 7))
+    assert_equal([[2, 2, 2, 2], [2, 3, 3], [3, 5]], combination_sum([2, 3, 5], 8))
+    assert_equal([], combination_sum([2], 1))
+  end
+end