M. Nguyen - Linked List

linked_list/linked_list.py

@@ -9,72 +9,162 @@ def __init__(self, value, next_node = None):
 # 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: 0(1)
+    # Space Complexity: 0(1)
     def get_first(self):
-        pass
 
+        if self.head == 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: 0(1)
+    # Space Complexity: 0(n)
     def add_first(self, value):
-        pass
+        node = Node(value, next_node=self.head)
+        self.head = 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: 0(n)
+    # Space Complexity: 0(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: 0(n)
+    # Space Complexity: 0(1)
     def length(self):
-        pass
+
+        count = 0
+
+        current = self.head
+
+        while current:
+
+            current = current.next
+            count += 1
+
+        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: 0(n)
+    # Space Complexity: 0(1)
     def get_at_index(self, index):
-        pass
+
+        if self.head == None:
+            return None
+
+        if index == 0:
+            return self.head.value
+
+        current = self.head
+        counter = 0
+
+        # index - 1 --> we are manipulating the pointer for the previous node
+        while current.next and counter < index - 1:
+            current = current.next
+            counter += 1
+
+        if current.next:
+            return current.next.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: 0(n)
+    # Space Complexity: 0(1)
     def get_last(self):
-        pass
+
+        if self.head == None:
+            return None
+
+        current = self.head
+        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: 0(n)
+    # Space Complexity: 0(1)
     def add_last(self, value):
-        pass
+
+        if self.head == None:
+            self.head = Node(value, None)
+            return 
+
+        current = self.head
+
+        while current.next:
+            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
+
+        if self.head == None:
+            return None
+
+        current = self.head
+        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: 0(n)
+    # Space Complexity: 0(1)
     def delete(self, value):
-        pass
+
+        if self.head == None:
+            return None
+
+
+        if self.head.value == value:
+            self.head = self.head.next
+            return
+
+        current = self.head
+
+        while current: 
+            if current.value == value:
+                break
+            previous = current
+            current = current.next
+
+        previous.next = current.next
+
 
     # method to print all the values in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: 0(n)
+    # Space Complexity: 0(1)
     def visit(self):
+
         helper_list = []
         current = self.head
 
@@ -83,14 +173,25 @@ def visit(self):
             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: 0(1)
+    # Space Complexity: 0(n)
     def reverse(self):
-        pass
-
+
+        previous = None
+        current = self.head
+
+        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: ?
@@ -126,3 +227,4 @@ def create_cycle(self):
             current = current.next
 
         current.next = self.head # make the last node link to first node
+