Monica Cruz - Maple C16

linked_list/linked_list.py

@@ -1,4 +1,3 @@
-
 # Defines a node in the singly linked list
 class Node:
 
@@ -13,67 +12,157 @@ def __init__(self):
 
     # 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
+        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)
+        new_node.next = 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_node = self.head
+        while current_node is not None:
+            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
+        node_count = 0
+        current_node = self.head
+        while current_node is not None:
+            node_count += 1
+            current_node = current_node.next
+        return node_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
+        current_node = self.head
+        current_index = 0
+
+        if current_node is None:
+            return None
+
+        while current_node is not None:
+            if current_index == index:
+                return current_node.value
+            else:
+                current_node = current_node.next
+                current_index+=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_node = self.head
+
+        if current_node is None:
+            return None
+
+        while True:
+            if current_node.next is None:
+                return current_node.value
+            else:
+                current_node = current_node.next
+
+
 
     # 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)
+        current_node = self.head
+
+        if current_node is None:
+            self.head = new_node
+            return
+
+        # What do I want while loop to do? I want while loop to find the last node 
+
+        while current_node is not None:
+            if current_node.next is None:
+                break
+            current_node = current_node.next 
+
+        # When last node is found, I want to append new_node to it.
+        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
+        current_node = self.head
+        if current_node is None:
+            return None
+
+        max_value = current_node.value
+
+        while current_node.next:
+            if current_node.value > max_value:
+                max_value = current_node.value
+            current_node = current_node.next
+
+        if current_node.value > max_value:
+            max_value = current_node.value
+
+        return max_value
 
     # 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_node = self.head
+        previous_node = None
+
+        if current_node is None:
+            return None
+
+        # Case: value to be deleted is the first value in the linked list
+        if current_node.value == value:
+            self.head = current_node.next
+            current_node = None
+            return
+
+        # Case: value to be deleted is the last value in the linked list
+            # traverse linked list to find the last node
+            # compare speficied value to last node's value
+            # if the values match, re-assign the penultimate node reference to None
+        while current_node is not None and current_node.value != value:
+            previous_node = current_node
+            current_node = current_node.next
+
+        previous_node.next = current_node.next
+        current_node = 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 +175,41 @@ 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(n)
     def reverse(self):
-        pass
-
+
+        # Put nodes in a list
+        # Reverse the list
+        # Create a new linked list from the reversed list
+
+        current_node = self.head
+        nodes_list = []
+        nodes_list_reverse = []
+
+        while current_node is not None:
+            nodes_list.append(current_node)
+            current_node = current_node.next
+
+        i = len(nodes_list)-1
+
+        while i > 0:
+            nodes_list_reverse.append(nodes_list[i])
+            i -= 1
+        nodes_list_reverse.append(nodes_list[0])
+
+        for i in range(0, len(nodes_list_reverse)):
+            if i == 0:
+                current_node = nodes_list_reverse[i]
+                self.head = current_node
+            else:
+                current_node = nodes_list_reverse[i]
+
+            if i < len(nodes_list_reverse)-1:
+                current_node.next = nodes_list_reverse[i+1]
+
+        current_node.next = None
+
     ## Advanced/ Exercises
     # returns the value at the middle element in the singly linked list
     # Time Complexity: ?