2025-01-13 v. 7.9.7: added "895. Maximum Frequency Stack"

Author: fartem

README.md

@@ -666,3 +666,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 363. Max Sum of Rectangle No Larger Than K    | [Link](https://leetcode.com/problems/max-sum-of-rectangle-no-larger-than-k/)     | [Link](./lib/hard/363_max_sum_of_rectangle_no_larger_than_k.rb)    | [Link](./test/hard/test_363_max_sum_of_rectangle_no_larger_than_k.rb)    |
 | 458. Poor Pigs                                | [Link](https://leetcode.com/problems/poor-pigs/)                                 | [Link](./lib/hard/458_poor_pigs.rb)                                | [Link](./test/hard/test_458_poor_pigs.rb)                                |
 | 871. Minimum Number of Refueling Stops        | [Link](https://leetcode.com/problems/minimum-number-of-refueling-stops/)         | [Link](./lib/hard/871_minimum_number_of_refueling_stops.rb)        | [Link](./test/hard/test_871_minimum_number_of_refueling_stops.rb)        |
+| 895. Maximum Frequency Stack                  | [Link](https://leetcode.com/problems/maximum-frequency-stack/)                   | [Link](./lib/hard/895_maximum_frequency_stack.rb)                  | [Link](./test/hard/test_895_maximum_frequency_stack.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 = '7.9.6'
+  s.version = '7.9.7'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'

lib/hard/895_maximum_frequency_stack.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/maximum-frequency-stack/
+class FreqStack
+  # Init
+  def initialize
+    @freq = {}
+    @group = {}
+    @max_freq = 0
+  end
+
+  # @param {Integer} val
+  # @return {Void}
+  def push(val)
+    f = @freq.fetch(val, 0) + 1
+    @freq[val] = f
+
+    @max_freq = f if f > @max_freq
+
+    if @group.key?(f)
+      @group[f] << val
+    else
+      @group[f] = [val]
+    end
+  end
+
+  # @return {Integer}
+  def pop
+    stack = @group[@max_freq]
+    x = stack.delete_at(stack.size - 1)
+    @freq[x] = @freq[x] - 1
+
+    @max_freq -= 1 if @group[@max_freq].size.zero?
+
+    x
+  end
+end

test/hard/test_895_maximum_frequency_stack.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/hard/895_maximum_frequency_stack'
+require 'minitest/autorun'
+
+class MaximumFrequencyStackTest < ::Minitest::Test
+  def test_default_one
+    freq_stack = ::FreqStack.new
+    freq_stack.push(5)
+    freq_stack.push(7)
+    freq_stack.push(5)
+    freq_stack.push(7)
+    freq_stack.push(4)
+    freq_stack.push(5)
+
+    assert_equal(5, freq_stack.pop)
+    assert_equal(7, freq_stack.pop)
+    assert_equal(5, freq_stack.pop)
+    assert_equal(4, freq_stack.pop)
+  end
+end