Rock - N.Lucuab

linked_list/linked_list.py

@@ -9,71 +9,161 @@ def __init__(self, value, next_node = None):
 # 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
 
     # 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) - nothing new is being added, so memory is unaffected
     def get_first(self):
-        pass
+        # if the list is empty, return none
+        if self.head == None:
+            return None
+        # if the list is not empty, return the value of the head
+        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)? Only 1 node is being added, so 0(1) sounds right memory-wise
     def add_first(self, value):
-        pass
+        self.head = Node(value, next_node=self.head)
 
     # 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) - traverses the whole list
+    # Space Complexity: O(1) - nothing new is being added, so memory is unaffected
     def search(self, value):
-        pass
+        current = self.head
+
+        while current:
+            if current.value == value:
+                return True
+            current = current.next
+        return False
 
     # method that returns the length of the singly linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n) - traverses the list
+    # Space Complexity: O(1) - no new node is being added, so memory is unaffected
     def length(self):
-        pass
+        current = self.head
+        # set variable to 0, to initiate counter
+        list_length = 0
+        while current != None: 
+            # add to counter 
+            list_length += 1
+            # set current to next to traverse
+            current = current.next
+        # return list_length when while loops breaks 
+        return list_length
 
     # 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) - traverses the list to find value
+    # Space Complexity: O(1) - no new node is being added, so memory is unaffected
     def get_at_index(self, index):
-        pass
+        current = self.head
+        # return None if fewer nodes (can be equal!) than index value
+        if index >= self.length():
+            return None
+        count = 0
+        # check count versus index
+        while current != None: 
+            if count == index: 
+                return current.value
+            # set current to next 
+            current = current.next
+            # increment count
+            count += 1
 
     # 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) - traverses list? 
+    # Space Complexity: O(1) - no new node is being added, so memory is unaffected
     def get_last(self):
-        pass
+        current = self.head
+        while current != None:
+            # if next is None, end of list, so return value
+            if current.next == None:
+                return current.value
+            else: 
+                # set current to next, if next != None
+                current = current.next
+        # if list is empty return None
+        return None
 
     # method that inserts a given value as a new last node in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(1) - only inserts 1 value
+    # Space Complexity: O(n) - traverses the list in order to find the end, and then adds on value
     def add_last(self, value):
-        pass
+        # can set new_node to head, in the case of an empty list. That value also becomes 'last'
+        new_node = Node(value)
+        current = self.head
+        if current == None:
+            self.head = new_node
+            return
+        # set current to next, while not currently at end of list
+        while current.next != None:
+            current = current.next
+        # set current.next to the new_node
+        current.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
+        # set up an empty variable
+        max_value = 0
+        current = self.head
+        # check if list empty, if so, we can return None
+        if current == None: 
+            return None
+        # when list is not empty, check current value against value in max_value
+        # if max_value is less than current value, set max_value to the current value
+        while current != None: 
+            if max_value < current.value:
+                max_value = current.value
+            # set current to next to traverse
+            current = current.next
+        # return max_value when loop breaks
+        return max_value
 
     # method to delete the first node found with specified value
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n) - traverses list to find specified value
+    # Space Complexity: O(1) - deletes only 1 value
     def delete(self, value):
-        pass
+        current = self.head
+        previous = None
+        # check if list is empty
+        if current == None: 
+            return
+
+        # if not empty...
+        while current != None:
+            # check current value against passed in value
+            if current.value == value:
+                # if equal, check to see if end of list
+                if current.next == None:
+                    previous.next = None
+                    return previous
+                # set current value equal to the next node value
+                current.value = current.next.value
+                # set current next to the NEXT node
+                current.next = current.next.next
+                # continue loop 
+                continue
+                # return current
+            # set previous equal to the current node
+            previous = current
+            # increment current
+            current = current.next
+        return current
+
 
     # method to print all the values in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n) - traverses list
+    # Space Complexity: O(n) - prints out every value
     def visit(self):
         helper_list = []
         current = self.head
@@ -86,11 +176,21 @@ 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) - traverses/reverses entire list
+    # Space Complexity: O(1) - no new nodes are being added
     def reverse(self):
-        pass
-
+        previous = None
+        current = self.head
+        next_node = current.next
+
+        # reversing node order
+        while current != None:
+            next_node = current.next
+            current.next = previous
+            previous = current
+            current = next_node
+        self.head = previous
+
     ## Advanced/ Exercises
     # returns the value at the middle element in the singly linked list
     # Time Complexity: ?