Abigail C - Rock

linked_list/linked_list.py

@@ -1,128 +1,236 @@
 
 # Defines a node in the singly linked list
+from typing import Counter
+
+
 class Node:
 
-    def __init__(self, value, next_node = None):
+    def __init__(self, value, next_node=None):
         self.value = value
         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
+        self.head = None  # keep the head private. Not accessible outside this class
+        # self.end = 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 == None:
+            return None
+        else:
+            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, next_node=self.head)
+        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 = 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
+        length = 0
+
+        while current:
+            length += 1
+            current = current.next
+        return 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)
+    # Space Complexity: O(1)
     def get_at_index(self, index):
-        pass
+        current = self.head
+        current_index = 0
+
+        while current:
+            if current_index == index:
+                return current.value
+            current_index += 1
+            current = current.next
+        if current_index < index:
+            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
+
+        while current:
+            if current.next == None:
+                return current.value
+            current = current.next
 
     # 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
+        new_node = Node(value)
+
+        if self.head == None:
+            self.head = new_node
+            return new_node
+        else:
+            last = self.head
+            while last.next:
+                last = last.next
+            last.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
+        current = self.head
+        if current == None:
+            return None
+        max_value = current.value
+        while current != None:
+            if max_value < current.value:
+                max_value = current.value
+            current = current.next
+        return max_value
 
     # method to delete the first node found with specified value
-    # Time Complexity: ?
-    # Space Complexity: ?
-    def delete(self, value):
-        pass
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
+    def delete(self, val):
+        current = self.head
+        previous = None
+
+        while current != None:
+            if current.value == val:
+                if current.next == None:
+                    previous.next = None
+                    return previous
+                current.value = current.next.value
+                current.next = current.next.next
+                continue
+                # return current
+            previous = current
+            current = current.next
+        return current
 
     # 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
 
         while current:
             helper_list.append(str(current.value))
             current = current.next
-        
+
         print(", ".join(helper_list))
 
     # 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
-
+        previous = None
+        current = self.head
+        future = current.next
+
+        while current != None:
+            future = current.next
+            current.next = previous
+            previous = current
+            current = future
+        self.head = previous
+
     ## Advanced/ Exercises
     # returns the value at the middle element in the singly linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def find_middle_value(self):
-        pass
+        current = self.head
+        count = 0
+
+        while current != None:
+            count += 1
+            current = current.next
+        middle = int(count/2)
 
-    # find the nth node from the end and return its value
-    # assume indexing starts at 0 while counting to n
-    # Time Complexity: ?
-    # Space Complexity: ?
+        current = self.head
+        for i in range(0,middle+1):
+            if i == middle:
+                return current.value
+            current = current.next
+        return self.head
+
+    # # find the nth node from the end and return its value
+    # # assume indexing starts at 0 while counting to n
+    # # Time Complexity: O(n)
+    # # Space Complexity: O(1)
     def find_nth_from_end(self, n):
-        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.
-    # returns true if a cycle is found, false otherwise.
-    # Time Complexity: ?
-    # Space Complexity: ?
-    def has_cycle(self):
-        pass
-
-    # Helper method for tests
-    # 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
+        current = self.head
+        count = 0
 
-        # navigate to last node
+        while current != None:
+            current = current.next
+            count += 1
+
+        if n > count-1:
+            return None
+
         current = self.head
-        while current.next != None:
+        for i in range(0,count):
+            if (count-1)-i == n:
+                return current.value
             current = current.next
+        return self.head
+
+    # # # checks if the linked list has a cycle. A cycle exists if any node in the
+    # # # linked list links to a node already visited.
+    # # # returns true if a cycle is found, false otherwise.
+    # # # Time Complexity: ?
+    # # # Space Complexity: ?
+    # def has_cycle(self):
+    #     pass
+
+
+
+    # # # Helper method for tests
+    # # # 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
+    #     current.next = self.head # make the last node link to first node