diff --git a/linked_list/linked_list.py b/linked_list/linked_list.py index 63993214..a4276b71 100644 --- a/linked_list/linked_list.py +++ b/linked_list/linked_list.py @@ -13,105 +13,199 @@ 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: + return self.head.value + return None # 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(n) def add_first(self, value): - pass + new_first = Node(value, self.head) + new_first.next_node = self.head + self.head = new_first + # 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 = self.head + found = False + while found is False and current is not None: + if current.value == value: + found = True + else: + current = current.next + return found + # 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 = self.head + length = 0 + while current: + length += 1 + current = current.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 + current = self.head + i = 0 + while i < index and current is not None: + i += 1 + current = current.next + if i == index: + return current.value + 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 = self.head + if not current: + return None + 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: O(n) + # Space Complexity: O(1) def add_last(self, value): - pass + new_last = Node(value) + if self.head is None: + self.head = new_last + return + else: + current = self.head + while current.next is not None: + current = current.next + current.next = new_last + # method to return the max value in the linked list # returns the data value and not the node def find_max(self): - pass + current = self.head + if current is None: + return None + max = current.value + while current: + if max < current.value: + max = current.value + current = current.next + return max + # method to delete the first node found with specified value - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # (should be able to be done in O(1) if just getting rid of pointer?) + # Space Complexity: O(1) def delete(self, value): - pass + current = self.head + if current: + if current.value == value: + self.head = current.next + current = None + return + while current: + if current.value == value: + break + previous = current + current = current.next + if current == None: + return + previous.next = current.next + current = 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 - while current: helper_list.append(str(current.value)) 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: O(n) + # Space Complexity: O(1) def reverse(self): - pass + previous = None + current = self.head + while current is not None: + 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: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def find_middle_value(self): - pass + if not self.head: + return None + + return self.get_at_index(int(self.length()/2)) + # find the nth node from the end and return its value # assume indexing starts at 0 while counting to n - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def find_nth_from_end(self, n): - pass + current = self.head + if not current: + return None + len = self.length() - 1 + if n > len: + return + for i in range(0, len - 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: ? + # Time Complexity: O(n) + # Space Complexity: O(n) def has_cycle(self): - pass + current = self.head + visited = set() + if current == None: + return False + while current.next != None: + visited.add(current) + current = current.next + if current in visited: + return True + return False # Helper method for tests # Creates a cycle in the linked list for testing purposes diff --git a/tests/linked_list_test.py b/tests/linked_list_test.py index 58a9d0cf..270064a0 100644 --- a/tests/linked_list_test.py +++ b/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