diff --git a/linked_list/linked_list.py b/linked_list/linked_list.py index 63993214..1828c184 100644 --- a/linked_list/linked_list.py +++ b/linked_list/linked_list.py @@ -7,73 +7,146 @@ def __init__(self, value, next_node = None): self.next = next_node # Defines the singly linked list + + class LinkedList: def __init__(self): 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 + 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: O(1) + # Space Complexity: O(1) def add_first(self, value): - pass + new_node = Node(value) + new_node.next = self.head + self.head = new_node + + return self.head.value # 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 + + 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: O(n) + # Space Complexity: O(1) def length(self): - pass + current = self.head + count = 0 + + while current != None: + count += 1 + current = current.next + + 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: O(n) + # Space Complexity: O(1) def get_at_index(self, index): - pass + i = 0 + current = self.head + + while current: + if i == index: + return current.value + current = current.next + i += 1 + + 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 self.head: + return None + + # keep looping until end of the links + 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(1) + # Space Complexity: O(1) def add_last(self, value): - pass + current = self.head + + if current is None: + self.head = Node(value, None) + else: + while current: + if current.next == None: + break + 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 + current = self.head + if current is None: + return None + 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: O(n) + # Space Complexity: O(1) def delete(self, value): - pass + current = self.head + prev = None + if not current: + return None + + while current: + if current.value == value: + if current == self.head: + self.head = current.next + return + prev.next = current.next + return + prev = current + current = current.next # 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 @@ -86,24 +159,34 @@ 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 + current = self.head + previous = None + + 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: ? # Space Complexity: ? def find_middle_value(self): - pass + pass # find the nth node from the end and return its value # assume indexing starts at 0 while counting to n # Time Complexity: ? # Space Complexity: ? def find_nth_from_end(self, n): - pass + pass + # checks if the linked list has a cycle. A cycle exists if any node in the # linked list links to a node already visited. @@ -117,12 +200,4 @@ def has_cycle(self): # Creates a cycle in the linked list for testing purposes # Assumes the linked list has at least one node def create_cycle(self): - if self.head == None: - return - - # navigate to last node - current = self.head - while current.next != None: - current = current.next - - current.next = self.head # make the last node link to first node + pass \ No newline at end of file