Diana - Pine

linked_list/linked_list.py

@@ -1,79 +1,159 @@
 
 # Defines a node in the singly linked list
-class Node:
+from types import new_class
+
 
- def __init__(self, value, next_node = None):
+class Node:
+ def __init__(self, value, next_node = None, prev_node = None):
  self.value = value
  self.next = next_node
+ self.previous = prev_node #This line because this is a doubly linked list
 
 # Defines the singly linked list
 class LinkedList:
  def __init__(self):
- self.head = None # keep the head private. Not accessible outside this class
+ self.head = None # keep the head private. Not accessible outside this class
+ self.tail = None
 
  # returns the value in the first node
  # returns None if the list is empty
- # Time Complexity: ?
- # Space Complexity: ?
+ # Time Complexity: O(1)
+ # Space Complexity: O(1)
  def get_first(self):
- pass
-
+ if self.head is None:
+ return None
+ return self.head.value
 
  # method to add a new node with the specific data value in the linked list
  # insert the new node at the beginning of the linked list
- # Time Complexity: ?
- # Space Complexity: ?
+ # Time Complexity: O(1)
+ # Space Complexity: O(1)
  def add_first(self, value):
- pass
+ if self.head is None:
+ self.head = self.tail = Node(value)
+
+ else:
+ new_node = Node(value, self.head)
+ self.head.previous = new_node
+ self.head = new_node
 
  # method to find if the linked list contains a node with specified value
  # returns true if found, false otherwise
- # Time Complexity: ?
- # Space Complexity: ?
+ # Time Complexity: O(n)
+ # Space Complexity: O(1)
  def search(self, value):
- pass
+ current_node = self.head
+
+ if current_node == None:
+ return False
+
+ while current_node: 
+ if current_node.value == value:
+ return True
+ current_node = current_node.next
+ return False
 
  # method that returns the length of the singly linked list
- # Time Complexity: ?
- # Space Complexity: ?
+ # Time Complexity: O(n)
+ # Space Complexity: O(1)
  def length(self):
- pass
+ len_ll = 0
+ current_node = self.head
+
+ while current_node != None:
+ len_ll +=1
+ current_node = current_node.next
+ return len_ll
 
  # method that returns the value at a given index in the linked list
  # index count starts at 0
  # returns None if there are fewer nodes in the linked list than the index value
- # Time Complexity: ?
- # Space Complexity: ?
+ # Time Complexity: O(n)
+ # Space Complexity: O(1)
  def get_at_index(self, index):
- pass
+ count = 0
+ current_node = self.head
+
+ while current_node != None:
+ if count == index:
+ return current_node.value
+ count += 1
+ current_node = current_node.next
+ return None
 
  # method that returns the value of the last node in the linked list
  # returns None if the linked list is empty
- # Time Complexity: ?
- # Space Complexity: ?
+ # Time Complexity: O(n)
+ # Space Complexity: O(1)
  def get_last(self):
- pass
+ head = self.head
+ if head == None:
+ return None
+
+ while head.next:
+ head = head.next
+
+ return head.value
 
  # method that inserts a given value as a new last node in the linked list
- # Time Complexity: ?
- # Space Complexity: ?
+ # Time Complexity: O(n)
+ # Space Complexity: O(1)
  def add_last(self, value):
- pass
+ if self.head == None:
+ self.add_first(value)
+ else:
+ new_node = Node(value)
+ current_node = self.head
+
+ while current_node.next:
+ current_node = current_node.next
+ current_node.next = new_node
+
 
  # method to return the max value in the linked list
  # returns the data value and not the node
  def find_max(self):
- pass
+ if self.head == None:
+ return None
+
+ head = self.head
+ max_value = self.get_at_index(0)
+
+ while head:
+ if head.value > max_value:
+ max_value = head.value
+ head = head.next
+
+ return max_value
 
  # method to delete the first node found with specified value
- # Time Complexity: ?
- # Space Complexity: ?
+ # Time Complexity: O(n)
+ # Space Complexity: O(n)
  def delete(self, value):
- pass
+
+ new = self.head
+
+ if new != None:
+ if new.value == value:
+ self.head = new.next
+ new = None
+ return
+
+ while new:
+ if new.value == value:
+ break
+ prev = new
+ new = new.next
+ if new == None:
+ return
+
+ prev.next = new.next
+ new = None
+
 
  # method to print all the values in the linked list
- # Time Complexity: ?
- # Space Complexity: ?
+ # Time Complexity: O(n)
+ # Space Complexity: O(1)
  def visit(self):
  helper_list = []
  current = self.head
@@ -86,11 +166,22 @@ def visit(self):
 
  # method to reverse the singly linked list
  # note: the nodes should be moved and not just the values in the nodes
- # Time Complexity: ?
- # Space Complexity: ?
+ # Time Complexity: O(n)
+ # Space Complexity: O(1)
  def reverse(self):
- pass
-
+ if not self.head:
+ return
+ current_node = self.head
+ previous_node = None
+
+ while current_node:
+ next = current_node.next
+ current_node.next = previous_node
+ previous_node = current_node
+ current_node = next
+
+ self.head = previous_node
+
  ## Advanced/ Exercises
  # returns the value at the middle element in the singly linked list
  # Time Complexity: ?