Add solution for challenge #2

Author: Mauricio Klein

README.md

@@ -1,3 +1,4 @@
 # Challenges list
 
 - [x] [Challenge 1: Spirally traversing a matrix](challenge-1/README.md)
+- [x] [Challenge 2: Largest subset whose all elements are Fibonacci numbers](challenge-2/README.md)

challenge-2/Gemfile

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+# Gemfile
+source "https://rubygems.org"
+
+gem "rspec"

challenge-2/Gemfile.lock

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+GEM
+  remote: https://rubygems.org/
+  specs:
+    diff-lcs (1.3)
+    rspec (3.8.0)
+      rspec-core (~> 3.8.0)
+      rspec-expectations (~> 3.8.0)
+      rspec-mocks (~> 3.8.0)
+    rspec-core (3.8.0)
+      rspec-support (~> 3.8.0)
+    rspec-expectations (3.8.2)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.8.0)
+    rspec-mocks (3.8.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.8.0)
+    rspec-support (3.8.0)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  rspec
+
+BUNDLED WITH
+   1.16.6

challenge-2/README.md

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+# Largest subset whose all elements are Fibonacci numbers
+
+The original challenge description can be found [here](https://www.geeksforgeeks.org/largest-subset-whose-all-elements-are-fibonacci-numbers/)
+
+## Description
+
+Given an array with positive number the task is that we find largest subset from array that contain elements which are Fibonacci numbers.
+
+## Examples
+
+```
+Input  : [1, 4, 3, 9, 10, 13, 7]
+Output : [1, 3, 13]
+```
+
+```
+Input  : [0, 2, 8, 5, 2, 1, 4, 13, 23]
+Output : [0, 2, 8, 5, 2, 1, 13, 23]
+```

challenge-2/lib/solver.rb

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+class Solver
+  def call(arr)
+    return [] if arr.empty?
+
+    max = arr.max
+    fib_lookup = generate_fib_lookup(max)
+    result = []
+
+    arr.each do |val|
+      if fib_lookup.has_key?(val)
+        result << val
+      end
+    end
+
+    result
+  end
+
+  private
+
+  def generate_fib_lookup(max)
+    lookup = {
+      0 => nil,
+      1 => nil
+    }
+
+    first, second = 1, 1
+    next_val = nil
+
+    while second < max
+      next_val = first + second
+      lookup[next_val] = nil
+
+      first = second
+      second = next_val
+    end
+
+    lookup
+  end
+end

challenge-2/spec/solver_spec.rb

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+require 'spec_helper'
+
+RSpec.describe Solver do
+  subject { described_class.new.call(arr) }
+
+  context "Test case 1" do
+    let(:arr) { [1, 4, 3, 9, 10, 13, 7] }
+    let(:expected_result) { [1, 3, 13] }
+
+    it { is_expected.to eq(expected_result) }
+  end
+
+  context "Test case 2" do
+    let(:arr) { [0, 2, 8, 5, 2, 1, 4, 13, 23] }
+    let(:expected_result) { [0, 2, 8, 5, 2, 1, 13] }
+
+    it { is_expected.to eq(expected_result) }
+  end
+
+  context "Test case 3" do
+    let(:arr) { (50..1000).to_a }
+    let(:expected_result) { [55, 89, 144, 233, 377, 610, 987] }
+
+    it { is_expected.to eq(expected_result) }
+  end
+
+  context "Test case 4" do
+    let(:arr) { [] }
+    let(:expected_result) { [] }
+
+    it { is_expected.to eq(expected_result) }
+  end
+end

challenge-2/spec/spec_helper.rb

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+Dir["#{__dir__}/../lib/*.rb"].each { |file| require file }