Mary Tian CS Fun Linked Lists

linked_list/linked_list.py

@@ -7,73 +7,146 @@ def __init__(self, value, next_node = None):
         self.next = next_node
 
 # Defines the singly linked list
+
+
 class LinkedList:
     def __init__(self):
       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)
     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
+        new_node = Node(value)
+        new_node.next = self.head
+        self.head = new_node
+
+        return self.head.value
 
     # 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 = 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)
+    # Space Complexity: O(1)
     def length(self):
-        pass
+        current = self.head
+        count = 0
+
+        while current != None:
+            count += 1
+            current = current.next
+
+        return count
 
     # 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
+        i = 0
+        current = self.head
+
+        while current:
+            if i == index:
+                return current.value
+            current = current.next
+            i += 1
+
+        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
+        current = self.head
+
+        if not self.head:
+            return None
+
+        # keep looping until end of the links
+        while current.next:
+            current = current.next
+
+        return current.value
 
     # method that inserts a given value as a new last node in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(1)
+    # Space Complexity: O(1)
     def add_last(self, value):
-        pass
+        current = self.head
+
+        if current is None:
+            self.head = Node(value, None)
+        else:
+            while current:
+                if current.next == None:
+                    break
+                current = current.next
+
+            current.next = Node(value, None)
 
     # method to return the max value in the linked list
     # returns the data value and not the node
     def find_max(self):
-        pass
+        current = self.head
+        if current is None:
+            return None
+        max = 0
+
+        while current:
+            if current.value > max:
+                max = current.value
+            current = current.next
+
+        return max
 
     # method to delete the first node found with specified value
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def delete(self, value):
-        pass
+        current = self.head
+        prev = None
+        if not current:
+            return None
+
+        while current:
+            if current.value == value:
+                if current == self.head:
+                    self.head = current.next
+                    return
+                prev.next = current.next
+                return
+            prev = current
+            current = current.next
 
     # method to print all the values in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(n)
     def visit(self):
         helper_list = []
         current = self.head
@@ -86,24 +159,34 @@ 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
+        current = self.head
+        previous = None
+
+        while current:
+            next = current.next
+            current.next = previous
+            previous = current
+            current = next
+
+        self.head = previous
 
     ## Advanced/ Exercises
     # returns the value at the middle element in the singly linked list
     # Time Complexity: ?
     # Space Complexity: ?
     def find_middle_value(self):
-        pass
+       pass
 
     # find the nth node from the end and return its value
     # assume indexing starts at 0 while counting to n
     # Time Complexity: ?
     # Space Complexity: ?
     def find_nth_from_end(self, n):
-        pass
+       pass
+
 
     # checks if the linked list has a cycle. A cycle exists if any node in the
     # linked list links to a node already visited.
@@ -117,12 +200,4 @@ def has_cycle(self):
     # Creates a cycle in the linked list for testing purposes
     # Assumes the linked list has at least one node
     def create_cycle(self):
-        if self.head == None:
-            return
-
-        # navigate to last node
-        current = self.head
-        while current.next != None:
-            current = current.next
-
-        current.next = self.head # make the last node link to first node
+       pass