Water - Kareha

lib/problems.rb

@@ -1,13 +1,43 @@
 require_relative './stack.rb'
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n*m)
+# Space Complexity: O(m), but also potentially O(1)
 def balanced(string)
-  raise NotImplementedError, "Not implemented yet"
+  # assumes these are only valid chars
+  hash_table = {"}" => "{", "]" => "[", ")" => "("}  # space: O(m)? maybe O(1) bc size of this doesnt grow with input?
+  stack = Stack.new
+
+  string.each_char do |char|                    # time: O(n)
+    if hash_table.has_value?(char)              # time: O(m)?
+      stack.push(char)
+    else
+      return false if stack.pop != hash_table[char]    # time: O(1)
+    end
+  end
+
+  return stack.empty?
 end
 
-# Time Complexity: ?
-# Space Complexity: ?
+
+# Time Complexity: O(n)
+# Space Complexity: O(m), but also potentially O(1)
 def evaluate_postfix(postfix_expression)
-  raise NotImplementedError, "Not implemented yet"
+  # assumes these are only valid operations
+  operations = {"*" => true, "+" => true, "/" => true, "-" => true}    # space: O(m), maybe O(1) bc size of this doesnt grow with input?
+  stack = Stack.new     
+  result = ""
+
+  postfix_expression.each_char do |char|    # time: O(n)
+    if operations[char]                     # time: O(1)
+      num2 = stack.pop.to_i                 # time: O(1)
+      num1 = stack.pop.to_i                 # time: O(1)
+      result = num1.method(char).(num2)
+      stack.push(result)                    # time: O(1), space: O(1)?? because will never be larger than 3 elements
+    else
+      stack.push(char)                      # time: O(1)
+    end
+  end
+
+  return result
+
 end

lib/queue.rb

@@ -1,31 +1,62 @@
 class Queue
 
+  SIZE = 20
+
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = Array.new(SIZE)
+    @front = @back = -1
   end
 
   def enqueue(element)
-    raise NotImplementedError, "Not yet implemented"
+
+    if @front == -1 && @back == -1
+      @front = @back = 0
+    elsif (@back + 1) % SIZE == @front
+      raise ArgumentError.new("Queue is full")
+    elsif @back == SIZE - 1
+      @back = 0
+    else
+      @back += 1
+    end
+
+    @store[@back] = element
   end
 
   def dequeue
-    raise NotImplementedError, "Not yet implemented"
+    raise ArgumentError, "Queue is empty" if @store.empty?
+
+    result = @store[@front] 
+    @store[@front] = nil
+    if @front == @back
+      @front = @back = -1
+    elsif @front == SIZE - 1
+      @front = 0
+    else
+      @front += 1
+    end
+    return result
   end
 
   def front
-    raise NotImplementedError, "Not yet implemented"
+    return @store[@front]
   end
 
   def size
-    raise NotImplementedError, "Not yet implemented"
+    return @store.select{|x| !x.nil?}.length
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    @store.map{|x| x.nil?}.all?
   end
 
   def to_s
-    return @store.to_s
+    queue = []
+    20.times do |i|
+      index = (i + @front) % SIZE
+      queue.push(@store[index]) if @store[index]
+    end
+
+    return queue.to_s
   end
-end
+
+end

lib/stack.rb

@@ -1,19 +1,18 @@
 class Stack
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = LinkedList.new
   end
 
   def push(element)
-    raise NotImplementedError, "Not yet implemented"
+    @store.add_first(element)
   end
 
   def pop
-    raise NotImplementedError, "Not yet implemented"
+    @store.remove_first
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    @store.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
 

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"