Space - Nora

lib/problems.rb

@@ -1,9 +1,38 @@
 require_relative './stack.rb'
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n) - length of the string
+# Space Complexity: O(n) - # of opening brackets
+
+# Given a string containing opening and closing braces, check if it represents a balanced expression or not.
 def balanced(string)
-  raise NotImplementedError, "Not implemented yet"
+  stack = Stack.new
+  opening = ["(", "[", "{"]
+
+  string.each_char do |char|
+    # if character is an opening bracket
+    if opening.include?(char)
+      # push to stack
+      stack.push(char)
+    # if not
+    else
+      # pop the top character from the stack
+      top_stack = stack.pop
+      if char == ')'
+        return false if top_stack != '('
+      elsif char == ']'
+        return false if top_stack != '['
+      elsif char == '}'
+        return false if top_stack != '{'
+        # if the current character is a closing bracket
+          # return false if the top stack character is not a matching open
+      end
+    end
+
+
+  end
+
+  # return true if the stack is empty, false if not
+  return stack.empty?
 end
 
 # Time Complexity: ?

lib/queue.rb

@@ -1,31 +1,63 @@
 class Queue
 
+# Using a circular buffer with an internal array starting at 20 elements, implement a Queue
+
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = Array.new(20)
+    @size = 20
+    @front = -1
+    @back = -1
   end
 
-  def enqueue(element)
-    raise NotImplementedError, "Not yet implemented"
+  # Adds the value to the back of the queue.
+  def enqueue(value)
+    if @front == -1
+      @front = 0
+      @back = 1
+      @store[@front] = value
+    elsif @store.empty?
+      raise ArgumentError, "Queue is full"
+    else
+      @store[@back] = value
+      @back = (@back + 1) % @size
+    end
   end
 
+  # removes and returns a value from the front of the queue
   def dequeue
-    raise NotImplementedError, "Not yet implemented"
+    if @front == -1
+      raise ArgumentError, "Queue is empty"
+    else
+      data = @store[@front]
+      @front = (@front + 1) % @size
+      if @store.empty?
+        @front = back = -1
+      end
+      return data
+    end
   end
 
-  def front
-    raise NotImplementedError, "Not yet implemented"
-  end
+  # def front
+  #   raise NotImplementedError, "Not yet implemented"
+  # end
 
-  def size
-    raise NotImplementedError, "Not yet implemented"
-  end
+  # def size
+  #   raise NotImplementedError, "Not yet implemented"
+  # end
 
+  # returns true if the queue is empty and false otherwise
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @front == @back
   end
 
   def to_s
-    return @store.to_s
+    list = []
+    current = @front
+
+    while current != @back
+      list << @store[current]
+      current = (current + 1) % @size
+    end
+    return list.to_s
   end
 end

lib/stack.rb

@@ -1,19 +1,24 @@
 class Stack
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = LinkedList.new
   end
 
-  def push(element)
-    raise NotImplementedError, "Not yet implemented"
+  # Adds the value to the top of the stack
+  def push(value)
+    @store.add_last(value)
   end
 
+  # Removes and returns an element from the top of the stack
   def pop
-    raise NotImplementedError, "Not yet implemented"
+    return nil if @store.empty?
+
+    @store.remove_last
   end
 
+  # returns true if the stack is empty and false otherwise
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return true if @store.empty?
+    return false # if not empty
   end
 
   def to_s

test/problems_test.rb

@@ -2,7 +2,7 @@
 
 Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
 
-xdescribe "Test wave 3 problems" do
+describe "Test wave 3 problems" do
   describe "balanced" do
     it "Given balanced strings it should return true" do
 
@@ -33,7 +33,7 @@
     end
   end
 
-  describe "postfix" do
+  xdescribe "postfix" do
     it "can add a 2 numbers together" do
 
       expect(evaluate_postfix("34+")).must_equal 7

test/test_helper.rb

@@ -10,4 +10,4 @@
 require_relative "../lib/queue.rb"
 require_relative "../lib/stack.rb"
 # Extra exercises
-# require_relative "../lib/problems.rb"
+require_relative "../lib/problems.rb"