start on array list

Author: jethrodaniel

ruby/lib/dsa.rb

@@ -5,6 +5,7 @@
 require_relative "dsa/deque"
 require_relative "dsa/binary_tree"
 require_relative "dsa/trie"
+require_relative "dsa/array_list"
 
 # Data structures and algorithms practice.
 module DSA

ruby/lib/dsa/array_list.rb

@@ -0,0 +1,56 @@
+module DSA
+  # An array list (a growable array).
+  #
+  class ArrayList
+    # @return [Integer]
+    attr_reader :capacity
+
+    # @return [Integer]
+    attr_reader :length
+
+    # @param capacity [Integer]
+    def initialize capacity: 100
+      raise ArgumentError, "capacity must be positive" unless capacity.positive?
+
+      @capacity = capacity
+      @length = 0
+      @array = Array.new(capacity) { nil }
+    end
+
+    # @param index [Integer]
+    # @return [T]
+    #
+    def [] index
+      raise ArgumentError, "index must be >= 0" if index.negative?
+
+      raise ArgumentError, "index out of bounds" if index > @length - 1
+
+      @length = index + 1 if index + 1 > @length
+
+      @array[index]
+    end
+
+    # @param index [Integer]
+    # @param item [T]
+    # @return [T]
+    #
+    def []= index, item
+      raise ArgumentError, "index must be >= 0" if index.negative?
+
+      raise ArgumentError, "TODO" if index > @capacity
+
+      @length = index + 1 if index + 1 > @length
+
+      @array[index] = item
+    end
+
+    # @param item [T]
+    # @return [T]
+    #
+    def append item
+      @array[@length] = item
+      @length += 1
+      item
+    end
+  end
+end

ruby/spec/dsa/array_list_spec.rb

@@ -0,0 +1,92 @@
+RSpec.describe DSA::ArrayList do
+  describe "#initialize" do
+    it "errors if capacity is invalid" do
+      expect { described_class.new capacity: 0 }
+        .to raise_error(ArgumentError, "capacity must be positive")
+      expect { described_class.new capacity: -1 }
+        .to raise_error(ArgumentError, "capacity must be positive")
+    end
+  end
+
+  describe "#capacity" do
+    it "has a default capacity" do
+      list = described_class.new
+      expect(list.capacity).to eq 100
+    end
+
+    it "has an intial capacity" do
+      list = described_class.new capacity: 42
+      expect(list.capacity).to eq 42
+    end
+  end
+
+  describe "#length" do
+    it "returns the number of items in the list" do
+      list = described_class.new
+      expect(list.length).to eq 0
+
+      list[0] = 42
+      expect(list.length).to eq 1
+    end
+  end
+
+  describe "#[]" do
+    context "when index is invalid" do
+      it "errors" do
+        list = described_class.new
+        expect { list[-1] }.to raise_error(ArgumentError, "index must be >= 0")
+      end
+    end
+
+    context "when index is less than the length" do
+      it "returns the item at that index" do
+        list = described_class.new
+        list[0] = 42
+        expect(list[0]).to eq 42
+      end
+    end
+
+    context "when index is greater than or equal to the length" do
+      it "errors" do
+        list = described_class.new
+        list[0] = 42
+        expect { list[1] }.to raise_error(ArgumentError, "index out of bounds")
+      end
+    end
+  end
+
+  describe "#[]=" do
+    context "when index is invalid" do
+      it "errors" do
+        list = described_class.new
+        expect { list[-1] = 42 }.to raise_error(ArgumentError, "index must be >= 0")
+      end
+    end
+
+    context "when index is less than the capacity" do
+      it "sets the item at that index" do
+        list = described_class.new
+        list[0] = 42
+        expect(list[0]).to eq 42
+      end
+    end
+
+    context "when index is greater than or equal to the capacity" do
+      it "resizes the array and sets the item at that index" do
+        skip "TODO"
+      end
+    end
+  end
+
+  describe "#append" do
+    it "adds an item to the end of the list" do
+      list = described_class.new
+      list[0] = 1
+      list[1] = 2
+      list.append 42
+
+      expect(list[2]).to eq 42
+      expect(list.length).to eq 3
+    end
+  end
+end

ruby/spec/dsa_spec.rb

@@ -16,6 +16,7 @@
         "LICENSE.txt",
         "README.md",
         "lib/dsa.rb",
+        "lib/dsa/array_list.rb",
         "lib/dsa/binary_tree.rb",
         "lib/dsa/deque.rb",
         "lib/dsa/doubly_linked_list.rb",