Sarah Jane Olivas - Spruce - C16

linked_list/linked_list.py

@@ -1,79 +1,173 @@
 
 # Defines a node in the singly linked list
+
 class Node:
 
     def __init__(self, value, next_node = None):
         self.value = value
         self.next = next_node
 
 # Defines the singly linked list
+# Starting off a linked list is always constant time and space complexity.
 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)
     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
+
+        # more compact, not as readable, need to look at the constructor to understand
+        # self.head references the original linked list that the new head is assigned to
+        # self.head = Node(value, 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)
+    # Space Complexity: O(1)
     def search(self, value):
-        pass
+        # initialize a node pointer
+        current = self.head
+
+        while current != None:
+            if current.value == value:
+                return True  # Value was found
+
+            current = current.next
+
+        return False  # Value not found
 
     # 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
+        pointer = self.head
+        counter = 0
+
+        while pointer != None:
+            counter += 1
+            pointer = pointer.next
+
+        return counter
 
     # 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: 0(1)
     def get_at_index(self, index):
-        pass
+        if index < 0:
+            return None
+
+        current_index = 0
+        pointer = self.head
+
+        while pointer != None:
+            if current_index == index:
+                return pointer.value
+            pointer = pointer.next
+            current_index += 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)
+    # Space Complexity: O(1)
     def get_last(self):
-        pass
+        # pointer = self.head
+        # next_node = pointer.next
+
+        # while next_node != None:
+        #     pointer = next_node
+        #     next_node = pointer.next
+
+        if self.head is None:
+            return None
+
+        pointer = self.head
+
+        while pointer.next is not None:
+            pointer = pointer.next
+
+        return pointer.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
+        new_node = Node(value)
+
+        if self.head is None:
+            self.head = new_node
+            return
+
+        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
+        if self.head is None:
+            return None
+
+        pointer = self.head
+        maximum = self.head.value
+
+        while pointer is not None:
+            if maximum < pointer.value:
+                maximum = pointer.value
+            pointer = pointer.next
+
+        return maximum
+
 
     # 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
+        position = self.head
+
+        if position is not None:
+            if position.value == value:
+                self.head = position.next
+                position = None
+                return
+
+        while position is not None:
+            if position.value == value:
+                break
+            prev = position
+            position = position.next
+
+        if position == None:
+            return
+
+        prev.next = position.next
+        position = None
 
     # 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
@@ -86,11 +180,24 @@ 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
-
+        prev = None
+        current = self.head
+        next_node = current.next
+
+        while current:
+            current.next = prev
+            prev = current
+            current = next_node
+            if next_node:
+                next_node = next_node.next
+
+        self.head = prev
+
+# ======================================================================================
+
     ## Advanced/ Exercises
     # returns the value at the middle element in the singly linked list
     # Time Complexity: ?