Space - Hala

lib/problems.rb

@@ -1,13 +1,66 @@
-require_relative './stack.rb'
+require_relative 'stack'
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(N)
+# Space Complexity: O(N)
 def balanced(string)
-  raise NotImplementedError, "Not implemented yet"
+  strStack = Stack.new
+  string.each_char do |char|
+    if ['(', '[', '{'].include?(char)
+      strStack.push(char)
+    else
+      element = strStack.pop 
+      if char == ']' && element != '['
+        return false
+      elsif char == ')' && element != '('
+        return false
+      elsif char == '}' && element != '{'
+        return false  
+      end
+    end
+  end
+
+
+  return strStack.empty?
 end
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(N)
+# Space Complexity: O(N)
 def evaluate_postfix(postfix_expression)
-  raise NotImplementedError, "Not implemented yet"
+  postfix_stack = Stack.new
+
+  postfix_expression.each_char do |char|        
+    if numeric?(char)
+      postfix_stack.push(char.to_i)
+    else
+
+      num2 = postfix_stack.pop       
+      num1 = postfix_stack.pop
+
+      case char
+      when "+"   
+          answer = num1 + num2        
+      when "*"       
+          answer = num1* num2    
+      when "-"        
+          answer = num1- num2     
+      when "/"        
+          answer = num1/ num2    
+      end   
+
+      if answer== nil
+        postfix_stack.push(num2)
+        postfix_stack.push(num1)
+      else
+        postfix_stack.push(answer)
+        answer = nil
+      end
+    end
+  end
+
+  return postfix_stack.pop
+
+end
+
+def numeric?(char)
+  char =~ /[[:digit:]]/
 end

lib/queue.rb

@@ -1,31 +1,36 @@
+require_relative "linked_list"
+
 class Queue
 
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @list = LinkedList.new
   end
 
   def enqueue(element)
-    raise NotImplementedError, "Not yet implemented"
+    @list.add_last(element)
   end
 
   def dequeue
-    raise NotImplementedError, "Not yet implemented"
+    return nil if self.empty?
+
+    element = @list.remove_first
+
+    return element
   end
 
   def front
-    raise NotImplementedError, "Not yet implemented"
+    @list.get_first
   end
 
   def size
-    raise NotImplementedError, "Not yet implemented"
+    @list.length
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @list.empty?
   end
 
   def to_s
-    return @store.to_s
+    return @list.to_s
   end
 end

lib/stack.rb

@@ -1,22 +1,28 @@
+require_relative "linked_list"
+
 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?
+
+    element = @list.remove_first
+
+    return element
+
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @list.empty?
   end
 
   def to_s
-    return @store.to_s
+    return @list.to_s
   end
 end

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
 

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"