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gracexinran Feb 18, 2020
75653af
Fixed indentation
gracexinran Feb 18, 2020
867d2cf
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gracexinran Feb 18, 2020
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gracexinran Feb 18, 2020
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303 changes: 190 additions & 113 deletions lib/linked_list.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@
class Node
attr_reader :data # allow external entities to read value but not write
attr_accessor :next # allow external entities to read or write next node

def initialize(value, next_node = nil)
@data = value
@next = next_node
Expand All @@ -12,120 +12,197 @@ 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

# 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 find if the linked list contains a node with specified value
# returns true if found, false otherwise
def search(value)
raise NotImplementedError
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

# method to return the min value in the linked list
# returns the data value and not the node
def find_min
raise NotImplementedError
end


# method that returns the length of the singly linked list
def length
raise NotImplementedError
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
end

# method to print all the values in the linked list
def visit
raise NotImplementedError
end

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


## Advanced Exercises
# returns the value at the middle element in the singly linked list
def find_middle_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)
raise NotImplementedError
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
end


# Additional Exercises
# returns the value in the first node
# returns nil if the list is empty
def get_first
raise NotImplementedError
end

# method that inserts a given value as a new last node in the linked list
def add_last(value)
raise NotImplementedError
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
def initialize
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👍

@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)
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👍

@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)
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👍

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

# 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
curr = @head.next
until curr.nil?
max = curr.data if max < curr.data
curr = curr.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
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👍

return nil if @head.nil?
min = @head.data
curr = @head.next
until curr.nil?
min = curr.data if min > curr.data
curr = curr.next
end
return min
end


# method that returns the length of the singly linked list
def length
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👍

count = 0
return count if @head.nil?
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Do you need this line?

curr = @head
until curr.nil?
count += 1
curr = curr.next
end
return count
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)
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👍 Good use of your length method.

return nil if index < 0 || index >= self.length
curr = @head
index.times do
curr = curr.next
end
return curr.data
end

# method to print all the values in the linked list
def visit
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👍

return nil if @head.nil?
curr = @head
until curr.nil?
p curr.data
curr = curr.next
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

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

return nil if @head.nil?
if value == @head.data
@head = @head.next
else
prev = @head
curr = @head.next
until curr.data == value || curr.next.nil?
prev = curr
curr = curr.next
end
if curr.data == value
prev.next = curr.next
end
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

# 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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👍

return nil if @head.nil?
curr = @head
prev = nil
until curr.nil?
temp = curr.next
curr.next = prev
prev = curr
curr = temp
end
@head = prev
end

## Advanced Exercises
# returns the value at the middle element in the singly linked list
def find_middle_value
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👍 Nice uses of existing methods!

return nil if @head.nil?
return self.get_at_index(self.length/2)
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)
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👍 Why not use get_at_index?

return nil if @head.nil? || n > self.length - 1
curr = @head
res = @head
n.times do
curr = curr.next
end
until curr.next.nil?
curr = curr.next
res = res.next
end
return res.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
end

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

# method that inserts a given value as a new last node in the linked list
def add_last(value)
if @head.nil?
self.add_first(value)
else
curr = @head
until curr.next.nil?
curr = curr.next
end

current.next = @head # make the last node link to first node
curr.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
def get_last
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👍

return nil if @head.nil?
self.get_at_index(self.length - 1)
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
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