diff --git a/lib/linked_list.rb b/lib/linked_list.rb index 8dee5e8d..7838be56 100644 --- a/lib/linked_list.rb +++ b/lib/linked_list.rb @@ -19,54 +19,141 @@ 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 def add_first(value) - raise NotImplementedError + new_node = Node.new(value, @head) + @head = new_node end # method to find if the linked list contains a node with specified value # returns true if found, false otherwise def search(value) - raise NotImplementedError + return false if @head == nil + + current = @head + found = false + until current == nil + if current.data == value + found = true + break + end + + current = current.next + end + return found 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 + + until current == nil + if current.data > max + max = current.data + end + current = current.next + end + return max end # method to return the min value in the linked list # returns the data value and not the node def find_min - raise NotImplementedError + return nil if @head == nil + + current = @head + min = @head.data + while current != nil + if current.data < min + min = current.data + end + current = current.next + end + return min end # method that returns the length of the singly linked list def length - raise NotImplementedError + return 0 if @head == nil + + current = @head + length = 0 + until current == nil + length += 1 + current = current.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 def get_at_index(index) - raise NotImplementedError + current = @head + + index.times do + if current != nil + current = current.next + end + end + + if current != nil + return current.data + else + return nil + end end # method to print all the values in the linked list def visit - raise NotImplementedError + return nil if @head == nil + current = @head + + until current == nil + print current.data + current = current.next + end end # method to delete the first node found with specified value def delete(value) - raise NotImplementedError + return nil if @head == nil + + if @head.data == value + @head = @head.next + end + + curr = @head + prev = nil + + while curr != nil + if curr.data == value + prev.next = curr.next + end + prev = curr + curr = curr.next + end + return @head end # method to reverse the singly linked list # note: the nodes should be moved and not just the values in the nodes def reverse - raise NotImplementedError + return nil if @head == nil + current = @head + previous = nil + + while current != nil + next_value = current.next + current.next = previous + previous = current + current = next_value + end + + @head = previous end @@ -79,7 +166,25 @@ def find_middle_value # find the nth node from the end and return its value # assume indexing starts at 0 while counting to n def find_nth_from_end(n) - raise NotImplementedError + return nil if @head == nil + + answer_pointer = @head + scanning_pointer = answer_pointer + + n.times do + if scanning_pointer.next != nil + scanning_pointer = scanning_pointer.next + else + return nil + end + end + + until scanning_pointer.next == nil + answer_pointer = answer_pointer.next + scanning_pointer = scanning_pointer.next + end + + return answer_pointer.data end # checks if the linked list has a cycle. A cycle exists if any node in the @@ -94,18 +199,41 @@ def has_cycle # returns the value in the first node # returns nil if the list is empty def get_first - raise NotImplementedError + if @head == nil + return @head + else + return @head.data + end end # method that inserts a given value as a new last node in the linked list def add_last(value) - raise NotImplementedError + if @head == nil + add_first(value) + else + current = @head + previous = current + new_last_node = Node.new(value, nil) + + until current.next == nil + current = current.next + end + current.next = new_last_node + end end # method that returns the value of the last node in the linked list # returns nil if the linked list is empty def get_last - raise NotImplementedError + return nil if @head == nil + + current = @head + + until current.next == nil + current = current.next + end + + return current.data end # method to insert a new node with specific data value, assuming the linked @@ -123,7 +251,7 @@ def create_cycle # navigate to last node current = @head while current.next != nil - current = current.next + current = current.next end current.next = @head # make the last node link to first node diff --git a/test/linked_list_test.rb b/test/linked_list_test.rb index d169c9a0..7d9173f9 100644 --- a/test/linked_list_test.rb +++ b/test/linked_list_test.rb @@ -174,7 +174,7 @@ expect(@list.find_max).must_equal 10 expect(@list.find_min).must_equal 3 - # delete last node + # # delete last node @list.delete(10) expect(@list.get_first).must_equal 3 expect(@list.length).must_equal 3 @@ -182,7 +182,7 @@ expect(@list.find_max).must_equal 9 expect(@list.find_min).must_equal 3 - # delete fist node (requires updating head) + # # delete fist node (requires updating head) @list.delete(4) expect(@list.get_first).must_equal 3 expect(@list.length).must_equal 2