Nicole Washington:Maple

linked_list/linked_list.py

@@ -1,97 +1,197 @@
-
 # Defines a node in the singly linked list
 class Node:
 
-    def __init__(self, value, next_node = None):
+    def __init__(self, value, next_node=None):
         self.value = value
         self.next = next_node
 
+
+# composition relationship to class 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
 
     # returns the value in the first node
     # returns None if the list is empty
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: constant, no traversing needed
+    # Space Complexity: constant, no new data structures
     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: constant
+    # Space Complexity: constant
     def add_first(self, value):
-        pass
+        new_node = Node(value)
+        new_node.next = self.head  # assign current head of linked list to the
+        self.head = new_node  # assign new node to 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: linear
+    # Space Complexity: constant
     def search(self, value):
-        pass
+        if self.head is None:
+            return False
+        current_node = self.head
+        target_node = Node(value)
+
+        # traverse list til reach target node or end of list
+        while current_node:
+            if current_node.value == target_node.value:
+                return True
+            current_node = current_node.next
+        return False
 
     # method that returns the length of the singly linked list
     # Time Complexity: ?
     # Space Complexity: ?
     def length(self):
-        pass
+        if self.head is None:
+            return 0
+        current_node = self.head
+        length_of_list = 0
+
+        # traverse list til reach end, increment length while traversing.
+        while current_node:
+            length_of_list += 1
+            current_node = current_node.next
+
+        return length_of_list
 
     # 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: linear
+    # Space Complexity: constant
     def get_at_index(self, index):
-        pass
+        if index < 0 or self.length() < index:
+            return None
+        current_index = 0
+        current_node = self.head
+
+        # traverse list till reach index or end of list
+        while current_node:
+            # can add a condition to check the current node is less than index if above does not work
+            if current_index == index:
+                break
+            current_node = current_node.next
+            current_index += 1
+
+        return current_node.value
 
     # 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: linear
+    # Space Complexity: constant
     def get_last(self):
-        pass
+        if self.head is None:
+            return None
+        current_node = self.head
+        tail_node = current_node
+        prev_node = None
+
+        # traverse list till reach end.
+        while current_node:
+            prev_node = current_node
+            current_node = current_node.next
+        tail_node = prev_node
+        return tail_node.value
 
     # method that inserts a given value as a new last node in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: linear
+    # Space Complexity: constant
     def add_last(self, value):
-        pass
+        if self.head is None:
+            self.head = value
+            return
+
+        prev_node = None
+        current_node = self.head
+        new_tail_node = Node(value)
+
+        # traverse list till reach end.
+        while current_node:
+            prev_node = current_node
+            current_node = current_node.next
+        # re-assign nodes so last node we found becomes second to last pointing to new tail and new tail points to none
+        new_tail_node = prev_node
+        current_node.next = new_tail_node
+        new_tail_node.next = None
 
     # 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
+        current_node = self.head
+        max_node = current_node
+
+        while current_node:
+            if current_node.value > max_node.value:
+                max_node = current_node
+                current_node = current_node.next
+
+        return max_node.value
 
     # method to delete the first node found with specified value
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: linear
+    # Space Complexity: constant
     def delete(self, value):
-        pass
+        if self.head is None:
+            return
+        current_node = self.head
+        next_node = current_node.next
+        target_value = value
+        if current_node.value == target_value:
+            current_node = current_node.next
+            return
+        while current_node:
+            if next_node.value == target_value:
+                current_node.next = next_node.next
+                return
+            current_node = current_node.next
+            next_node = next_node.next
+        return
 
     # method to print all the values in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: linear
+    # Space Complexity: linear
     def visit(self):
-        helper_list = []
-        current = self.head
+        node_values = []
+        current_node = self.head
 
-        while current:
-            helper_list.append(str(current.value))
-            current = current.next
-
-        print(", ".join(helper_list))
+        # traverse list,append values along the way.
+        while current_node:
+            node_values.append(str(current_node.value))
+            current_node = current_node.next
+        print(",".join(node_values))
 
     # 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: linear
+    # Space Complexity: constant
     def reverse(self):
-        pass
-
-    ## Advanced/ Exercises
+        if self.head is None:
+            return
+        current_node = self.head
+        next_node = None
+        prev_node = None
+
+        # traverse list, reversing pointers along the way
+        while current_node:
+            next_node = current_node.next
+            current_node.next = prev_node
+            prev_node = current_node
+            current_node = next_node
+        self.head = prev_node
+
+        ## Advanced/ Exercises
+
     # returns the value at the middle element in the singly linked list
     # Time Complexity: ?
     # Space Complexity: ?
@@ -125,4 +225,4 @@ def create_cycle(self):
         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