Diana - Space

lib/problems.rb

@@ -1,9 +1,36 @@
 require_relative './stack.rb'
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n), will always have to traverse through the string
+# Space Complexity: O(n), because in the worst case all char in string
+# are opening brackets, best case would be O(1) where we push and pop every item
 def balanced(string)
-  raise NotImplementedError, "Not implemented yet"
+  return false if string.nil?
+
+  string_stack = Stack.new
+
+  # Traversal of string
+  string.each_char { |char|
+    # push to stack if the character is an opening brace
+    if char == '{' or char == '[' or char == '('
+      string_stack.push(char)
+    else
+      # pop brace from stack and compare 
+      # char, return false if character doesn't match
+      current_char = string_stack.pop()
+      case current_char
+      when '('
+        return false if char != ')'
+      when '{'
+        return false if char != '}'
+      when '['
+        return false if char != ']'
+      end
+    end
+  }
+
+  # if stack is empty, return true
+  # else return false since it's unbalanced
+  string_stack.empty? ? true : false
 end
 
 # Time Complexity: ?

lib/queue.rb

@@ -1,31 +1,61 @@
 class Queue
 
-  def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+  attr_accessor :ring, :front, :back, :size
+
+  def initialize(size=20)
+    @size = size
+    @ring = Array.new(size)
+    @front = 0
+    @back = 0
   end
 
   def enqueue(element)
-    raise NotImplementedError, "Not yet implemented"
+    # if circular buffer is full, return empty array
+    return [] if (@back + 1) % @size == @front
+
+    # otherwise, add element to the back
+    @ring[@back] = element
+
+    # change @back to next free position, clockwise
+    @back = (@back + 1) % @size
   end
 
   def dequeue
-    raise NotImplementedError, "Not yet implemented"
+    return [] if @ring.empty?
+
+    dequeued_element = @ring[@front]
+    # dequeue by reassigning the front to the next position, clockwise
+    @front = (@front + 1) % @size
+
+    return dequeued_element
   end
 
   def front
-    raise NotImplementedError, "Not yet implemented"
+    @front
   end
 
   def size
-    raise NotImplementedError, "Not yet implemented"
+    @size
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    @back == @front
   end
 
   def to_s
-    return @store.to_s
+    return [] if @ring.empty?
+
+    ring_output = []
+    current_element = @front
+
+    while current_element != @back
+      # only get elements that are not nil
+      ring_output << @ring[current_element]
+
+      # shift to next element clockwise
+      current_element = (current_element + 1) % @size
+    end
+
+    return ring_output.to_s
   end
 end

lib/stack.rb

@@ -1,19 +1,20 @@
 class Stack
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @list = LinkedList.new
   end
 
   def push(element)
-    raise NotImplementedError, "Not yet implemented"
+    @list.add_first(element)
   end
 
   def pop
-    raise NotImplementedError, "Not yet implemented"
+    return nil if self.empty?
+
+    @list.remove_first
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @list.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

@@ -9,5 +9,6 @@
 require_relative "../lib/linked_list.rb"
 require_relative "../lib/queue.rb"
 require_relative "../lib/stack.rb"
+require_relative '../lib/problems.rb'
 # Extra exercises
 # require_relative "../lib/problems.rb"