Roza -cedar, re-submission including the comprehension questions

stacks_queues/linked_list.py

@@ -2,7 +2,7 @@
 class EmptyListError(Exception):
     pass
 
-# Defines a node in the singly linked list
+# Defines a node in the doubly linked list
 class Node:
     def __init__(self, value, next_node = None, previous_node = None):
         self.value = value
@@ -22,11 +22,13 @@ def __init__(self):
     # Space Complexity O(1)
     def add_first(self, value):
         new_node = Node(value)
-        new_node.next = self.head
-
         if self.head:
+            old_head = self.head
             self.head.previous = new_node
-        self.head = new_node
+            self.head = new_node
+            new_node.next = old_head
+        else:
+            self.head = new_node
         if not self.tail:
             self.tail = self.head
 
@@ -240,16 +242,15 @@ def get_last(self):
 
     def __str__(self):
         values = []
-
         current = self.head
         while current:
             values.append(str(current.value))
             current = current.next
 
         return ", ".join(values)
 
-ll = LinkedList()
-ll.add_first(5)
-ll.add_first(25)
-ll.add_last(1)
-print(ll)
+# ll = LinkedList()
+# ll.add_first(5)
+# ll.add_first(25)
+# ll.add_last(1)
+# print(ll)

stacks_queues/queue.py

@@ -1,4 +1,7 @@
 
+from tracemalloc import start
+
+
 INITIAL_QUEUE_SIZE = 20
 
 class QueueFullException(Exception):
@@ -13,7 +16,8 @@ def __init__(self):
         self.store = [None] * INITIAL_QUEUE_SIZE
         self.buffer_size = INITIAL_QUEUE_SIZE
         self.front = -1
-        self.rear = -1
+        self.rear = -1 
+        # -1 is just a marker to indicate nothing in the list, we can mark as None as well
         self.size = 0
 
 
@@ -23,39 +27,68 @@ def enqueue(self, element):
             In the store are occupied
             returns None
         """
-        pass
+        if self.size == self.buffer_size:
+            raise QueueFullException('Queue is full!')
+
+        if self.size == 0:
+            self.front = 0
+            self.rear = 0
+        self.store[self.rear] = element #insert where rear and front were pointing at first. But rear is the one moving to indicate the position of insert
+        self.rear = (self.rear + 1) % self.buffer_size #the next insert position
+        self.size += 1
 
     def dequeue(self):
         """ Removes and returns an element from the Queue
             Raises a QueueEmptyException if 
             The Queue is empty.
         """
-        pass
+        if self.empty():
+            raise QueueEmptyException
+        front_element = self.store[self.front]
+        self.store[self.front] = None
+        self.front = (self.front + 1) % self.buffer_size
+        self.size -= 1
+        return front_element
+        # check if empty, if so raise an exception
+        # find and store the front element
+        # move front to the next index
+        # return the old front elements
+        # front and rear are indexes, like 0, 1
 
     def front(self):
         """ Returns an element from the front
             of the Queue and None if the Queue
             is empty.  Does not remove anything.
         """
-        pass
+        return self.store[self.front]
 
 
     def size(self):
         """ Returns the number of elements in
             The Queue
         """
-        pass
+        return self.size
 
     def empty(self):
         """ Returns True if the Queue is empty
             And False otherwise.
         """
-        pass
+        return self.front == self.rear
 
     def __str__(self):
         """ Returns the Queue in String form like:
             [3, 4, 7]
             Starting with the front of the Queue and
             ending with the rear of the Queue.
         """
-        pass
+        queue_list = []
+        start_index = self.front
+        while (start_index % INITIAL_QUEUE_SIZE) < INITIAL_QUEUE_SIZE and len(queue_list) < self.size:
+            if self.store[start_index % INITIAL_QUEUE_SIZE] is not None:
+                queue_list.append(self.store[start_index % INITIAL_QUEUE_SIZE])
+                start_index += 1
+            else:
+                start_index += 1
+        return str(queue_list)
+
+

stacks_queues/stack.py

@@ -12,27 +12,35 @@ def push(self, element):
         """ Adds an element to the top of the Stack.
             Returns None
         """
-        pass
-
+        self.store.add_first(element)
+       
     def pop(self):
         """ Removes an element from the top
             Of the Stack
             Raises a StackEmptyException if
             The Stack is empty.
             returns None
         """
-        pass
+
+        return self.store.remove_first()
+
 
     def empty(self):
         """ Returns True if the Stack is empty
             And False otherwise
         """
-        pass
+        return self.store.empty()
 
     def __str__(self):
         """ Returns the Stack in String form like:
             [3, 4, 7]
             Starting with the top of the Stack and
             ending with the bottom of the Stack.
         """
-        pass
+        current = self.store.head
+        storeStacks = []
+        while current:
+            storeStacks.append(str(current.value))
+            current = current.next
+        return ", ".join(storeStacks)
+