Lilly C16 Pine

linked_list/linked_list.py

@@ -13,63 +13,140 @@ 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 == 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: ?
  def add_first(self, value):
- pass
+ 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: ?
  def search(self, value):
- pass
+ current = self.head 
+
+ while current != None:
+ 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: ?
  def length(self):
- pass
+ current = self.head
+
+ count = 0 
+ while current != None:
+ 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: ?
  def get_at_index(self, index):
- pass
+ current = self.head
+
+ count = 0 
+ while current:
+ if count == index:
+ return current.value 
+ count += 1
+ current = current.next
+
+ return None
+
+ # method that returns the index of the first node with the given value
+ # returns -1 if the value is not found in the linked list
+ # Time Complexity: O(n)?
+ # Space Complexity: O(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: ?
  def get_last(self):
- pass
+
+ if self.head == None:
+ return None
+
+ current = self.head 
+
+ while current.next != None:
+ 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: ?
+ #method to add node to the end of the linked list
  def add_last(self, value):
- pass
+ current = self.head
+ if current is None:
+ self.head = Node(value)
+ return
+ while current.next != None:
+ current = current.next
+ current.next = Node(value)
+
 
  # 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: ?
  def delete(self, value):
- pass
+ current = self.head
+
+ if current is not None:
+ if current.value == value:
+ self.head = current.next
+ temp = None
+ return
+
+ while current is not None:
+ if current.value == value:
+ break
+ prev = current
+ current = current.next
+
+ if current == None:
+ return None
+
+ prev.next = current.next
+
+ current = None
 
  # method to print all the values in the linked list
  # Time Complexity: ?
@@ -86,32 +163,84 @@ 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
+ while current is not None:
+ 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: ?
+ # find middle value of a singly linked list
  def find_middle_value(self):
- pass
+ if self.head == None:
+ return None
+
+ current = self.head
+ count = 0
+ while current:
+ count += 1
+ current = current.next
+
+ current = self.head
+ for i in range(count // 2):
+ current = current.next
+
+ return current.value
+
+
 
  # find the nth node from the end and return its value
  # assume indexing starts at 0 while counting to n
  # Time Complexity: ?
  # Space Complexity: ?
+ # find nth node from the end of the linked list
  def find_nth_from_end(self, n):
- pass
+ if self.head == None:
+ return None
+
+ current = self.head
+ count = 0
+ while current:
+ count += 1
+ current = current.next
+
+ current = self.head
+ for i in range(count - n):
+ current = current.next
+
+ return current.value
+
+
+
 
  # checks if the linked list has a cycle. A cycle exists if any node in the
  # linked list links to a node already visited.
  # returns true if a cycle is found, false otherwise.
  # Time Complexity: ?
  # Space Complexity: ?
  def has_cycle(self):
- pass
+ if self.head == None:
+ return False
+
+ current = self.head
+ visited = set()
+
+ while current:
+ if current in visited:
+ return True
+ visited.add(current)
+ current = current.next
+
+ return False
 
  # Helper method for tests
  # Creates a cycle in the linked list for testing purposes

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)
@@ -216,11 +216,11 @@ def test_find_middle_value_returns_element_at_index_two_of_six_element_list(list
  list.add_first(100)
  assert list.find_middle_value() == 60
 
-@pytest.mark.skip(reason="Going Further methods")
+# @pytest.mark.skip(reason="Going Further methods")
 def test_nth_from_n_when_list_is_empty(list):
  assert list.find_nth_from_end(3) == None
 
-@pytest.mark.skip(reason="Going Further methods")
+# @pytest.mark.skip(reason="Going Further methods")
 def test_find_nth_from_n_when_length_less_than_n(list):
  list.add_first(5)
  list.add_first(4)
@@ -230,7 +230,7 @@ def test_find_nth_from_n_when_length_less_than_n(list):
 
  assert list.find_nth_from_end(6) == None
 
-@pytest.mark.skip(reason="Going Further methods")
+# @pytest.mark.skip(reason="Going Further methods")
 def test_find_nth_from_n(list):
  list.add_first(1)
  list.add_first(2)
@@ -243,7 +243,7 @@ def test_find_nth_from_n(list):
  assert list.find_nth_from_end(3) == 4
  assert list.find_nth_from_end(4) == None
 
-@pytest.mark.skip(reason="Going Further methods")
+# @pytest.mark.skip(reason="Going Further methods")
 def test_has_cycle(list):
  assert list.has_cycle() == False