diff --git a/linked_list/linked_list.py b/linked_list/linked_list.py index 63993214..3c30cd2f 100644 --- a/linked_list/linked_list.py +++ b/linked_list/linked_list.py @@ -13,67 +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 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 + if self.head is None: + self.head = Node(value) + else: + new_node = Node(value, next_node = self.head) + self.head = new_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: O(n) + # Space Complexity: O(1) def search(self, value): - pass + if self.head is None: + return False + 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 + if not self.head: + return 0 + current = self.head + count = 1 + while current: + if not current.next: + return count + current = current.next + count += 1 # 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 = self.head + current_index = 0 + while current_index < index: + if not current.next and current_index < index: + return None + current = current.next + current_index += 1 + return current.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 not self.head: + return None + current = self.head + while current: + if not current.next: + return current.value + 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 + if not self.head: + self.head = Node(value, next_node = None) + return + current = self.head + while current: + if not current.next: + current.next = Node(value, next_node = None) + return current.next + current = current.next # method to return the max value in the linked list # returns the data value and not the node def find_max(self): - pass + if not self.head: + return None + current = self.head + max_value = self.head.value + while current: + if current.value > max_value: + max_value = current.value + current = current.next + return max_value # 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 not self.head: + return + if self.head.value == value: + self.head = self.head.next + return + + current = self.head + previous = None + while current: + if not current.next and current.value == value: + previous.next = None + return + if current.value == value: + previous.next = current.next + return + previous = 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 @@ -86,10 +159,22 @@ 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 + if not self.head: + return + + previous = None + current = self.head + next = self.head.next + while next: + current.next = previous + previous = current + current = next + next = next.next + current.next = previous + self.head = current ## Advanced/ Exercises # returns the value at the middle element in the singly linked list