Leaves - Bri

lib/problems.rb

@@ -1,13 +1,46 @@
 require_relative './stack.rb'
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n)
+# Space Complexity: O(n)
 def balanced(string)
-  raise NotImplementedError, "Not implemented yet"
+  # is it evenly divided by 2? If yes, then return false
+  # equal number of open parans and close parens
+  # make a new stack, make balanced = true
+  # go through each string using each_char
+  # if open parens, push to stack
+  # if close parens, check if stack has this match. If yes, pop off match in stack
+  # if at end, stack is empty, it is balanced. If parens remains, it is not balanced
+
+  if string.length % 2 == 1
+    return false 
+  end
+
+  stack = Stack.new
+
+  string.each_char do |char|
+    if char == '('
+      stack.push '('
+    elsif char == ')' && stack.pop != '('
+      return false 
+    end
+
+    if char == '{'
+      stack.push '}'
+    elsif char == '}' && stack.pop != '{'
+      return false 
+    end
+
+    if char == '['
+      stack.push '['
+    elsif char == ']' && stack.pop != '['
+      return false  
+    end
+  end
+  return true
 end
 
 # Time Complexity: ?
 # Space Complexity: ?
-def evaluate_postfix(postfix_expression)
-  raise NotImplementedError, "Not implemented yet"
-end
+# def evaluate_postfix(postfix_expression)
+#   raise NotImplementedError, "Not implemented yet"
+# end

lib/queue.rb

@@ -1,16 +1,17 @@
+require 'linked_list.rb'
+
 class Queue
 
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = LinkedList.new
   end
 
   def enqueue(element)
-    raise NotImplementedError, "Not yet implemented"
+    @store.add_last(element)
   end
 
   def dequeue
-    raise NotImplementedError, "Not yet implemented"
+    return @store.remove_first
   end
 
   def front
@@ -22,7 +23,7 @@ def size
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @store.empty?
   end
 
   def to_s

lib/stack.rb

@@ -1,19 +1,20 @@
+require 'linked_list.rb'
+
 class Stack
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = LinkedList.new
   end
 
   def push(element)
-    raise NotImplementedError, "Not yet implemented"
+    @store.add_last(element) 
   end
 
   def pop
-    raise NotImplementedError, "Not yet implemented"
+    return @store.remove_last
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @store.empty?  
   end
 
   def to_s