diff --git a/lib/linked_list.rb b/lib/linked_list.rb index 0de1ee00..ac7209c9 100644 --- a/lib/linked_list.rb +++ b/lib/linked_list.rb @@ -18,98 +18,176 @@ 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: ? - def add_first(value) - raise NotImplementedError - end - + # Time Complexity: 0(1) + # Space Complexity: 0(1) + + def add_first(value) + @head = Node.new(value, @head) + return @head + end + # new_node = Node.new(value) + # new_node.next = @head + # @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:0(n) with n being the length of the list + # Space Complexity:0(n) def search(value) - raise NotImplementedError + return false if @head.nil? + + current = @head + while (current.next != nil && current.data != value) do + current = current.next + if current.data != value + return false + end + end + return true end # method to return the max value in the linked list # returns the data value and not the node def find_max - raise NotImplementedError + return nil if @head.nil? + + current = @head + max = current.data + while (current.next != nil) + current = current.next + if current.data > max + max = current.data + end + 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: 0(n) with n being the length of the list + # Space Complexity: 0(n) def find_min - raise NotImplementedError + return nil if @head.nil? + + current = @head + min = current.data + while (current.next != nil) + current = current.next + if current.data < min + min = current.data + end + end + return min end # method that returns the length of the singly linked list - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: 0(n) with n being the length + # Space Complexity: 0(n) def length - raise NotImplementedError + current_node = @head + length = 0 + return 0 if @head.nil? + + while (!current_node.nil?) + current_node = current_node.next + length += 1 + 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: 0(n) with n being the length of the list + # Space Complexity: 0(n) def get_at_index(index) - raise NotImplementedError + return nil if @head.nil? + current = @head + index.times do + return nil if current.next.nil? + current = current.next + end + return current.data end # method to print all the values in the linked list - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: 0(n) with n being the length of the list + # Space Complexity: 0(n) def visit - raise NotImplementedError + current = @head + if current = current.data + return current.data + end end + # method to delete the first node found with specified value - # Time Complexity: ? + # Time Complexity: 0(n) with n being the length of the list # Space Complexity: ? def delete(value) - raise NotImplementedError + # if head is nil - return + if @head.nil? + return + end + # delete head if needed + if @head.data == value + @head = @head.next + return + end + + current_node = @head + while (current_node.next != nil ) + if current_node.next.data == value + current_node.next = current_node.next.next + return + end + current_node = current_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: 0(n) n being the length of the list + # Space Complexity: 0(n) def reverse - raise NotImplementedError + return if @head.nil? + current = @head + previous_node = nil + while (!current.nil?) + temp = current.next + current.next = previous_node + previous_node = current + current = temp + end + @head = previous_node end + end ## Advanced Exercises # returns the value at the middle element in the singly linked list # Time Complexity: ? # Space Complexity: ? - def find_middle_value - raise NotImplementedError - end + # def find_middle_value + # 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: ? - def find_nth_from_end(n) - raise NotImplementedError - end + # def find_nth_from_end(n) + # 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: ? # Space Complexity: ? - def has_cycle - raise NotImplementedError - end + # def has_cycle + # end # Additional Exercises @@ -117,45 +195,45 @@ def has_cycle # returns nil if the list is empty # Time Complexity: ? # Space Complexity: ? - def get_first - raise NotImplementedError - end + # def get_first + + # end # method that inserts a given value as a new last node in the linked list # Time Complexity: ? # Space Complexity: ? - def add_last(value) - raise NotImplementedError - end + # def add_last(value) + + # 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: ? - def get_last - raise NotImplementedError - end + # def get_last + + # end # method to insert a new node with specific data value, assuming the linked # list is sorted in ascending order # Time Complexity: ? # Space Complexity: ? - def insert_ascending(value) - raise NotImplementedError - end + # def insert_ascending(value) + + # end # Helper method for tests # Creates a cycle in the linked list for testing purposes # Assumes the linked list has at least one node - def create_cycle - return if @head == nil # don't do anything if the linked list is empty + # def create_cycle + # return if @head == nil # don't do anything if the linked list is empty # navigate to last node - current = @head - while current.next != nil - current = current.next - end - - current.next = @head # make the last node link to first node - end -end +# current = @head +# while current.next != nil +# current = current.next +# end + +# current.next = @head # make the last node link to first node +# end +# end