Paper - Kaylyn

linked_list/linked_list.py

@@ -9,71 +9,150 @@ 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: O(1)
+    # Space Complexity: O(1)
     def get_first(self):
-        pass
-
+        return None if self.head is None else 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, self.head)
+
+        self.head = new_node
+
+        return 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
+        current_node = self.head
+
+        while current_node:
+            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
+        current_node = self.head
+        length = 0
+
+        while current_node:
+            length += 1
+            current_node = current_node.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
+        if self.head is None:
+            return None
+
+        current_node = self.head
+        i = 0
+        while i < index and current_node:
+            current_node = current_node.next
+            i+=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: O(n)
+    # Space Complexity: O(1)
     def get_last(self):
-        pass
+        if self.head is None:
+            return None
+
+        current = self.head
+
+        while current:
+            if current.next is None:
+                return current.value
+            else:
+                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(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_node = self.head
+
+        while last_node.next:
+            last_node = last_node.next 
+
+        last_node.next = new_node
 
     # method to return the max value in the linked list
     # returns the data value and not the node
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def find_max(self):
-        pass
+        if self.head is None:
+            return None
+
+        current = self.head
+        max = self.head.value
+
+        while current.next:
+            if current.next.value > max:
+                max = current.next.value
+                current = current.next
+            else:
+                current = current.next
+
+        return max
 
     # 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
+        if self.head is None:
+            return None
+
+        current = self.head
+        if current.value == value:
+            self.head = current.next
+            return
+
+        while current: 
+            if current.value == value:
+                current = current.next
+                return
+
+            prev = current
+            current = current.next
+            if current.value == value:
+                prev.next = current.next
+                return
 
+
     # 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
@@ -86,17 +165,34 @@ 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 = None
+
+        while current:
+            next = current.next
+            current.next = prev
+            prev = current
+            current = next
+        self.head = prev
+
+
     ## 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
+        slow = self.head
+        fast = self.head
+
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+
+        return slow.value
 
     # find the nth node from the end and return its value
     # assume indexing starts at 0 while counting to n

tests/linked_list_test.py

@@ -197,7 +197,7 @@ def test_reverse_will_reverse_five_element_list(list):
     for i in range(0, 5):
         assert list.get_at_index(i) == i
 
-@pytest.mark.skip(reason="Going Further methods")
+# @pytest.mark.skip(reason="Going Further methods")
 def test_find_middle_value_returns_middle_element_of_five_element_list(list):
     list.add_first(10)
     list.add_first(30)
@@ -206,7 +206,7 @@ def test_find_middle_value_returns_middle_element_of_five_element_list(list):
     list.add_first(20)
     assert list.find_middle_value() == 50
 
-@pytest.mark.skip(reason="Going Further methods")
+# @pytest.mark.skip(reason="Going Further methods")
 def test_find_middle_value_returns_element_at_index_two_of_six_element_list(list):
     list.add_first(10)
     list.add_first(30)