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256 changes: 174 additions & 82 deletions lib/linked_list.rb
Original file line number Diff line number Diff line change
Expand Up @@ -12,120 +12,212 @@ def initialize(value, next_node = nil)

# Defines the singly linked list
class LinkedList
def initialize
@head = nil # keep the head private. Not accessible outside this class
end
def initialize
@head = nil # keep the head private. Not accessible outside this class
end

# 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
end
# 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)

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👍


# method to find if the linked list contains a node with specified value
# returns true if found, false otherwise
def search(value)
raise NotImplementedError
end
# new_node = Node.new(value)
# new_node.next = @head
# @head = new_node

# method to return the max value in the linked list
# returns the data value and not the node
def find_max
raise NotImplementedError
end
@head = Node.new(value, @head)
end

# method to return the min value in the linked list
# returns the data value and not the node
def find_min
raise NotImplementedError
# method to find if the linked list contains a node with specified value
# returns true if found, false otherwise
def search(value)

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current = @head
until current.nil?
return true if current.data == value
current = current.next
end
return false
end


# method that returns the length of the singly linked list
def length
raise NotImplementedError
# method to return the max value in the linked list
# returns the data value and not the node
def find_max

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return nil if @head.nil?
max = @head.data
current = @head.next
until current.nil?
if current.data > max
max = current.data
end
current = current.next
end
return max
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
# method to return the min value in the linked list
# returns the data value and not the node
def find_min

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return nil if @head.nil?
min = @head.data
current = @head.next
until current.nil?
if current.data < min
min = current.data
end
current = current.next
end
return min
end

# method to print all the values in the linked list
def visit
raise NotImplementedError
# method that returns the length of the singly linked list
def length

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length = 0
current = @head
until current.nil?
length += 1
current = current.next
end
return length
end

# method to delete the first node found with specified value
def delete(value)
raise NotImplementedError
# 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)

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current_index = 0
current = @head
until current_index == index
if current == nil
return nil
end
current = current.next
current_index += 1
end
return current.data
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
# method to print all the values in the linked list
def visit
current = @head
until current.nil?
puts current.data
current = current.next
end
end

# method to delete the first node found with specified value
def delete(value)

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👍 Nice!

return nil if @head.nil?
current = @head
previous = nil

## Advanced Exercises
# returns the value at the middle element in the singly linked list
def find_middle_value
raise NotImplementedError
until current.data == value
previous = current
current = current.next
end

# 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
if previous.nil?
@head = current.next
else
previous.next = current.next
end
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
# method to reverse the singly linked list
# note: the nodes should be moved and not just the values in the nodes
def reverse

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current = @head
previous = nil
until current.nil?
temp = current.next
current.next = previous
previous = current
current = temp
end

@head = previous
end

# Additional Exercises
# returns the value in the first node
# returns nil if the list is empty
def get_first
raise NotImplementedError
end
## Advanced Exercises
# returns the value at the middle element in the singly linked list
def find_middle_value
raise NotImplementedError
end
Comment on lines +141 to +143

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Just noting this isn't implemented


# method that inserts a given value as a new last node in the linked list
def add_last(value)
raise NotImplementedError
end
# 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)
return nil if @head.nil?
current = @head

# 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
length = 0
until current.next.nil?
length += 1
current = current.next
Comment on lines +151 to +154

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Why not use the existing length method?

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
return nil if n > length
current = @head
(length - n).times do |i|
current = current.next
end
return current.data
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
# 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
end

# Additional Exercises
# returns the value in the first node
# returns nil if the list is empty
def get_first
return @head ? @head.data : nil

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Nice use of a ternary

end

# navigate to last node
# method that inserts a given value as a new last node in the linked list
def add_last(value)

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if @head.nil?
add_first(value)
else
current = @head
while current.next != nil
current = current.next
until current.next == nil
current = current.next
end
current.next = Node.new(value)
end
end

current.next = @head # make the last node link to first node
# method that returns the value of the last node in the linked list
# returns nil if the linked list is empty
def get_last

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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
# list is sorted in ascending order
def insert_ascending(value)
raise NotImplementedError
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

# 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