diff --git a/lib/linked_list.rb b/lib/linked_list.rb index 8dee5e8d..0aecb6e0 100644 --- a/lib/linked_list.rb +++ b/lib/linked_list.rb @@ -19,99 +19,270 @@ 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 + # raise NotImplementedError + @head = Node.new(value, @head) + 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 + # raise + current = @head + until current.nil? + return true if current.data == value + current = current.next + end + return false end + # method to return the max value in the linked list # returns the data value and not the node def find_max - raise NotImplementedError - end + # raise NotImplementedError + current = @head + return nil if current.nil? + + max = @head + + until current.nil? + if current.data > max.data + max = current + end + current = current.next + end + + return max.data + end + # method to return the min value in the linked list # returns the data value and not the node def find_min - raise NotImplementedError - end + # raise NotImplementedError + return nil if @head.nil? + current = @head + min = @head.data + + until 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 + # raise NotImplementedError + size = 0 + current = @head + + until current.nil? + current = current.next + size = size + 1 + end + + + return size 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 + # raise NotImplementedError + current = @head + + index.times do + return nil if current.nil? + current = current.next + end + return current.data + end # method to print all the values in the linked list def visit - raise NotImplementedError + # raise NotImplementedError + 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 + # raise NotImplementedError + current = @head + return nil if current.nil? + + + previous = nil + + until current.data == value + return nil if current.nil? + previous = current + current = current.next + end + + if previous.nil? + @head = current.next + else + previous.next = current.next + end 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 + # raise NotImplementedError + return if @head.nil? + + current = @head + previous = nil + + until current.next.nil? + temp = current.next + current.next = previous + previous = current + current = temp + end + current.next = previous + @head = current end + ## Advanced Exercises # returns the value at the middle element in the singly linked list def find_middle_value - raise NotImplementedError + # raise NotImplementedError + length = self.length + if length % 2 == 0 + value = (length / 2) - 1 + else + value = (length / 2) + end + end + # fast = @root + # slow = @root + # until fast.nil? + # 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 + # raise NotImplementedError + current = @head + return nil if current.nil? + + + nth_head = @head + + n.times do + return nil if nth_head.next.nil? + nth_head = nth_head.next + end + + until nth_head.next.nil? + return current.data if current.next.nil? + current = current.next + nth_head = nth_head.next + end + return current.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. def has_cycle - raise NotImplementedError + # raise NotImplementedError + return if @head == nil + + current.next = @head end + + # Additional Exercises # returns the value in the first node # returns nil if the list is empty def get_first - raise NotImplementedError + # raise NotImplementedError + if @head.nil? + return nil + 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 + # raise NotImplementedError + current = @head + + if current.nil? + @head = Node.new(value) + return @head + end + + until current.next.nil? + current = current.next + end + current.next = Node.new(value) 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 + # raise NotImplementedError + current = @head + return nil if current.nil? + + + + 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 # list is sorted in ascending order def insert_ascending(value) - raise NotImplementedError + # raise NotImplementedError + return nil if @head.nil? + + current = @head + if value < current.data + self.first(value) + end + + until current.next.nil? + current_value = current.data + next_value = current.next.data + + if value > current_value && value < next_value + new_node = Node.new(value, current.next) + current.next = new_node + return + end + current = current.next + end + self.last(value) end # Helper method for tests @@ -129,3 +300,24 @@ def create_cycle current.next = @head # make the last node link to first node end end + +# def has_cycle +# fast = @head.next +# fast = fast.next if fast +# slow = @head + +# until fast.nil? || slow.nil +# if fast == slow +# return true +# end +# fast = fast.next +# return true if fast == slow +# fast = fast.next unless fast.nil? +# slow = slow.next +# end +# end + + + + + diff --git a/test/linked_list_test.rb b/test/linked_list_test.rb index d169c9a0..3ff24c00 100644 --- a/test/linked_list_test.rb +++ b/test/linked_list_test.rb @@ -1,6 +1,6 @@ require 'minitest/autorun' require 'minitest/reporters' -require 'minitest/skip_dsl' +# require 'minitest/skip_dsl' require_relative 'test_helper'