From c4aaa749a6356028817e3cf4599df04205aba81d Mon Sep 17 00:00:00 2001
From: fartem <jaman.smlnsk@gmail.com>
Date: Tue, 18 Mar 2025 07:36:32 +0300
Subject: [PATCH] 2025-03-18 v. 9.0.1: added "2121. Intervals Between Identical
 Elements"

---
 README.md                                     |  1 +
 leetcode-ruby.gemspec                         |  2 +-
 ...21_intervals_between_identical_elements.rb | 33 +++++++++++++++++++
 ...21_intervals_between_identical_elements.rb | 25 ++++++++++++++
 4 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 lib/medium/2121_intervals_between_identical_elements.rb
 create mode 100644 test/medium/test_2121_intervals_between_identical_elements.rb

diff --git a/README.md b/README.md
index 85312e48..d741b4cf 100644
--- a/README.md
+++ b/README.md
@@ -735,6 +735,7 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 2096. Step-By-Step Directions From a Binary Tree Node to Another                    | [Link](https://leetcode.com/problems/step-by-step-directions-from-a-binary-tree-node-to-another/)                    | [Link](./lib/medium/2096_step_by_step_directions_from_a_binary_tree_node_to_another.rb)                    | [Link](./test/medium/test_2096_step_by_step_directions_from_a_binary_tree_node_to_another.rb)                    |
 | 2109. Adding Spaces to a String                                                     | [Link](https://leetcode.com/problems/adding-spaces-to-a-string/)                                                     | [Link](./lib/medium/2109_adding_spaces_to_a_string.rb)                                                     | [Link](./test/medium/test_2109_adding_spaces_to_a_string.rb)                                                     |
 | 2116. Check if a Parentheses String Can Be Valid                                    | [Link](https://leetcode.com/problems/check-if-a-parentheses-string-can-be-valid/)                                    | [Link](./lib/medium/2116_check_if_a_parentheses_string_can_be_valid.rb)                                    | [Link](./test/medium/test_2116_check_if_a_parentheses_string_can_be_valid.rb)                                    |
+| 2121. Intervals Between Identical Elements                                          | [Link](https://leetcode.com/problems/intervals-between-identical-elements/)                                          | [Link](./lib/medium/2121_intervals_between_identical_elements.rb)                                          | [Link](./test/medium/test_2121_intervals_between_identical_elements.rb)                                          |
 | 2425. Bitwise XOR of All Pairings                                                   | [Link](https://leetcode.com/problems/bitwise-xor-of-all-pairings/)                                                   | [Link](./lib/medium/2425_bitwise_xor_of_all_pairings.rb)                                                   | [Link](./test/medium/test_2425_bitwise_xor_of_all_pairings.rb)                                                   |
 | 2429. Minimize XOR                                                                  | [Link](https://leetcode.com/problems/minimize-xor/)                                                                  | [Link](./lib/medium/2429_minimize_xor.rb)                                                                  | [Link](./test/medium/test_2429_minimize_xor.rb)                                                                  |
 | 2657. Find the Prefix Common Array of Two Arrays                                    | [Link](https://leetcode.com/problems/find-the-prefix-common-array-of-two-arrays/)                                    | [Link](./lib/medium/2657_find_the_prefix_common_array_of_two_arrays.rb)                                    | [Link](./test/medium/test_2657_find_the_prefix_common_array_of_two_arrays.rb)                                    |
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index 165932fc..16699ef5 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 = '9.0.0'
+  s.version = '9.0.1'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/medium/2121_intervals_between_identical_elements.rb b/lib/medium/2121_intervals_between_identical_elements.rb
new file mode 100644
index 00000000..6500694c
--- /dev/null
+++ b/lib/medium/2121_intervals_between_identical_elements.rb
@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/intervals-between-identical-elements/
+# @param {Integer[]} arr
+# @return {Integer[]}
+def get_distances(arr)
+  groups = ::Hash.new { |h, k| h[k] = [] }
+  arr.each_with_index { |num, idx| groups[num] << idx }
+  answer = ::Array.new(arr.size, 0)
+
+  groups.each_value do |indices|
+    n = indices.size
+
+    next if n == 1
+
+    prefix = [0]
+    sum = 0
+
+    indices.each do |x|
+      sum += x
+      prefix << sum
+    end
+
+    (0...n).each do |i|
+      current = indices[i]
+      left = current * i - prefix[i]
+      right = (prefix[n] - prefix[i + 1]) - current * (n - i - 1)
+      answer[current] = left + right
+    end
+  end
+
+  answer
+end
diff --git a/test/medium/test_2121_intervals_between_identical_elements.rb b/test/medium/test_2121_intervals_between_identical_elements.rb
new file mode 100644
index 00000000..85055d16
--- /dev/null
+++ b/test/medium/test_2121_intervals_between_identical_elements.rb
@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/medium/2121_intervals_between_identical_elements'
+require 'minitest/autorun'
+
+class IntervalsBetweenIdenticalElementsTest < ::Minitest::Test
+  def test_default_one
+    assert_equal(
+      [4, 2, 7, 2, 4, 4, 5],
+      get_distances(
+        [2, 1, 3, 1, 2, 3, 3]
+      )
+    )
+  end
+
+  def test_default_two
+    assert_equal(
+      [5, 0, 3, 4],
+      get_distances(
+        [10, 5, 10, 10]
+      )
+    )
+  end
+end