diff --git a/lib/linked_list.rb b/lib/linked_list.rb index 501c60fb..f6f05279 100644 --- a/lib/linked_list.rb +++ b/lib/linked_list.rb @@ -18,132 +18,279 @@ def initialize # 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(value) - raise NotImplementedError + node = Node.new(value, @head) + @head = node end # 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(value) - raise NotImplementedError + node = @head + + until node == nil + if node == value + return true + else + node = node.next + end + end + + return false end # method to return the max value in the linked list # returns the data value and not the node - # Time Complexity: - # Space Complexity + # Time Complexity: O(n) + # Space Complexity: O(1) def find_max - raise NotImplementedError + return nil if @head == nil + + node = @head + max = node.data + + until node == nil + if node.data > max + max = node.data + end + node = node.next + end + + return max end # method to return the min value in the linked list # returns the data value and not the node - # Time Complexity: - # Space Complexity + # Time Complexity: O(n) + # Space Complexity: O(1) def find_min - raise NotImplementedError + return nil if @head == nil + + node = @head + min = node.data + + until node == nil + if node.data < min + min = node.data + end + node = node.next + end + + return min end # method that returns the length of the singly linked list - # Time Complexity: - # Space Complexity + # Time Complexity: O(n) + # Space Complexity: O(1) def length - raise NotImplementedError + length = 0 + node = @head + + until node == nil + length += 1 + node = node.next + end + + return length end # method that returns the value at a given index in the linked list # index count starts at 0 # returns nil 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(index) - raise NotImplementedError + value = nil + node = @head + i = 0 + + until node == nil + if i == index + value = node.data + break + end + node = node.next + i += 1 + end + + return value end # method to print all the values in the linked list - # Time Complexity: - # Space Complexity + # Time Complexity: O(n) + # Space Complexity: O(1) def visit - raise NotImplementedError + return nil if @head == nil + node = @head + + until node == nil + puts node.data + node = node.next + end end # method to delete the first node found with specified value - # Time Complexity: - # Space Complexity + # Time Complexity: O(n) + # Space Complexity: O(1) def delete(value) - raise NotImplementedError + node = @head + + until node == nil + if node.data == value + @head = node.next + break + elsif node.next.data == value + node.next = node.next.next + break + end + node = node.next + end end # 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 - raise NotImplementedError + # 3 (head) -> 2 (tail) -> nil + return nil if !@head + + previous = nil + current = @head + + until !current + next_node = current.next # 2, nil + current.next = previous # nil, 3 @head + previous = current # 3 @head, 2 + current = next_node # 2, nil + end + + @head = previous #2 end ## Advanced Exercises # returns the value at the middle element in the singly linked list - # Time Complexity: - # Space Complexity + # Time Complexity: O(2n) -> O(n) + # Space Complexity: O(1) def find_middle_value - raise NotImplementedError + return nil if !@head + + node = @head + + length = self.length - 1 + length = (length / 2.0).ceil + + length.times do + node = node.next + end + + return node.data end # 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(2n) -> O(n) + # Space Complexity: O(1) def find_nth_from_end(n) - raise NotImplementedError + length = self.length + return nil if !(length > n) + + node = @head + + while n < length - 1 + node = node.next + n += 1 + end + + return node.data end # 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: + # Time Complexity: # Space Complexity def has_cycle raise NotImplementedError end - # Additional Exercises + # Additional Exercises # returns the value in the first node # returns nil if the list is empty - # Time Complexity: - # Space Complexity + # Time Complexity: O(1) + # Space Complexity: O(1) def get_first - raise NotImplementedError + node = @head + + return node == nil ? nil : node.data end # 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(value) - raise NotImplementedError + node = @head + + if node == nil + @head = Node.new(value) + else + until node.next == nil + node = node.next + end + + node.next = Node.new(value) + end end # method that returns the value of the last node in the linked list # returns nil if the linked list is empty - # Time Complexity: - # Space Complexity + # Time Complexity: O(n) + # Space Complexity: O(1) def get_last - raise NotImplementedError + node = @head + + return nil if node == nil + + until node.next == nil + node = node.next + end + + return node.data end # method to insert a new node with specific data value, assuming the linked # list is sorted in ascending order - # Time Complexity: - # Space Complexity + # Time Complexity: O(n) + # Space Complexity: O(1) def insert_ascending(value) - raise NotImplementedError + node = @head + + if node == nil + @head = Node.new(value) + elsif node.data > value + @head = Node.new(value, node) + else + while node.data < value + if node.next != nil + if node.next.data > value + connected_node = node.next + node.next = Node.new(value, connected_node) + break + end + node = node.next + else + node.next = Node.new(value) + break + end + end + end end # Helper method for tests @@ -160,4 +307,4 @@ def create_cycle current.next = @head # make the last node link to first node end -end +end \ No newline at end of file diff --git a/test/linked_list_test.rb b/test/linked_list_test.rb index 8311c439..e89e5634 100644 --- a/test/linked_list_test.rb +++ b/test/linked_list_test.rb @@ -15,7 +15,6 @@ describe 'initialize' do it 'can be created' do - # Assert expect(@list).must_be_kind_of LinkedList end