Add solution for challenge #1

Author: Mauricio Klein

README.md

@@ -0,0 +1,3 @@
+# Challenges list
+
+- [x] [Challenge 1: Spirally traversing a matrix](challenge-1/README.md)

challenge-1/Gemfile

@@ -0,0 +1,4 @@
+# Gemfile
+source "https://rubygems.org"
+
+gem "rspec"

challenge-1/Gemfile.lock

@@ -0,0 +1,26 @@
+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-1/README.md

@@ -0,0 +1,34 @@
+# Spirally traversing a matrix
+
+The original challenge description can be found [here](https://practice.geeksforgeeks.org/problems/spirally-traversing-a-matrix/0)
+
+## Description
+
+Given a 2D matrix of size M*N. Traverse and print the matrix in spiral form.
+
+## Input
+- Array of values
+- Dimension M (number of rows)
+- Dimension N (number of columns)
+
+## Output
+Elements when travelled in Spiral form, will be displayed in a single line.
+
+### Constraints:
+1 <=T<= 100
+
+2 <= M, N <= 10
+
+0 <= Ai <= 100
+
+### Example:
+
+```
+Input:
+  Array: [1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16]
+  M: 4
+  N: 4
+
+Output:
+  [1 2 3 4 8 12 16 15 14 13 9 5 6 7 11 10]
+```

challenge-1/lib/solver.rb

@@ -0,0 +1,52 @@
+class Solver
+  def call(arr, n_rows, n_columns)
+    length = n_rows * n_columns
+
+    row, col = 0, 0
+    inc_row, inc_col = 0, 1
+
+    result = Array.new(length)
+
+    length.times do |pos|
+      offset = calculate_offset(row, col, n_columns)
+
+      # Assign the element to result and
+      # mark the cell as visited (= nil)
+      result[pos] = arr[offset]
+      arr[offset] = nil
+
+      # If found a wall (end of array or visited cell),
+      # turn the walk diretion to the right
+      if wall?(arr, row + inc_row, col + inc_col, n_columns, n_rows)
+        inc_row, inc_col = turn_right(inc_row, inc_col)
+      end
+
+      # Update indexes
+      row += inc_row
+      col += inc_col
+    end
+
+    result
+  end
+
+  private
+
+  def calculate_offset(row, col, n_columns)
+    n_columns * row + col
+  end
+
+  def wall?(arr, row, col, n_columns, n_rows)
+    outbound?(row, n_rows) || outbound?(col, n_columns) || arr[calculate_offset(row, col, n_columns)].nil?
+  end
+
+  def outbound?(i, length)
+    i < 0 || i >= length
+  end
+
+  def turn_right(inc_row, inc_col)
+    return [ 1,  0] if inc_col == 1
+    return [ 0, -1] if inc_row == 1
+    return [-1,  0] if inc_col == -1
+           [ 0,  1]
+  end
+end

challenge-1/spec/solver_spec.rb

@@ -0,0 +1,61 @@
+require 'spec_helper'
+
+RSpec.describe Solver do
+  subject { described_class.new.call(arr, n_rows, n_columns) }
+
+  context "with 4x4 table" do
+    let(:arr) { (1..16).to_a }
+    let(:n_rows) { 4 }
+    let(:n_columns) { 4 }
+
+    it { is_expected.to eq([1, 2, 3, 4, 8, 12, 16, 15, 14, 13, 9, 5, 6, 7, 11, 10]) }
+  end
+
+  context "with 3x4 table" do
+    let(:arr) { (1..12).to_a }
+    let(:n_rows) { 3 }
+    let(:n_columns) { 4 }
+
+    it { is_expected.to eq([1, 2, 3, 4, 8, 12, 11, 10, 9, 5, 6, 7]) }
+  end
+
+  context "with 4x3 table" do
+    let(:arr) { (1..12).to_a }
+    let(:n_rows) { 4 }
+    let(:n_columns) { 3 }
+
+    it { is_expected.to eq([1, 2, 3, 6, 9, 12, 11, 10, 7, 4, 5, 8]) }
+  end
+
+  context "with 2x2 table" do
+    let(:arr) { (1..4).to_a }
+    let(:n_rows) { 2 }
+    let(:n_columns) { 2 }
+
+    it { is_expected.to eq([1, 2, 4, 3]) }
+  end
+
+  context "with 1x8 table" do
+    let(:arr) { (1..8).to_a }
+    let(:n_rows) { 1 }
+    let(:n_columns) { 8 }
+
+    it { is_expected.to eq([1, 2, 3, 4, 5, 6, 7, 8]) }
+  end
+
+  context "with 8x1 table" do
+    let(:arr) { (1..8).to_a }
+    let(:n_rows) { 8 }
+    let(:n_columns) { 1 }
+
+    it { is_expected.to eq([1, 2, 3, 4, 5, 6, 7, 8]) }
+  end
+
+  context "with empty table" do
+    let(:arr) { [] }
+    let(:n_rows) { 1 }
+    let(:n_columns) { 0 }
+
+    it { is_expected.to eq([]) }
+  end
+end

challenge-1/spec/spec_helper.rb

@@ -0,0 +1 @@
+Dir["#{__dir__}/../lib/*.rb"].each { |file| require file }