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Cynthia - Linked List #10

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Cynthia - Linked List #10

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5672490
making progress on many methods
cynthiacd Aug 17, 2017
1dc8836
all methods implemented and passing all tests
cynthiacd Aug 31, 2017
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186 changes: 171 additions & 15 deletions linked_list.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -4,9 +4,9 @@ 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)
def initialize(value, next_node=nil)
@data = value
@next = next
@next = next_node
end
end

Expand All @@ -19,77 +19,232 @@ 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 insert(value)
puts "Not implemented"
# puts "Not implemented"
# id node that new node should point to
if @head != nil
current = @head
@head = Node.new(value)
@head.next = current
else
@head = Node.new(value)
@head.next = nil
end
end

# method to find if the linked list contains a node with specified value
# returns true if found, false otherwise
def search(value)
puts "Not implemented"
current = @head

until current.next == nil
return true if current.value == value
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
puts "Not implemented"
current = @head
max = current.data

while current
max = current.data if current.data > max
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
puts "Not implemented"
current = @head
min = current.data

while current.next != nil
min = current.data if current.data < min
current = current.next
end

return min
end

# method that returns the length of the singly linked list
def length
puts "Not implemented"
length = 0
current = @head

while current
length += 1
current = current.next
end

return length
end

# method to return the value of the nth element from the beginning
# assume indexing starts at 0 while counting to n
def find_nth_from_beginning(n)
puts "Not implemented"
current = @head

n.times do
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)
puts "Not implemented"
current = @head
previous = nil
last = nil

until value < current.data
previous = current
current.next ? current = current.next : break
end

insert_node = Node.new(value)

if !current.next && value > current.data
current.next = insert_node
else
insert_node.next = current
previous.next = insert_node
end
end

# method to print all the values in the linked list
def visit
puts "Not implemented"
current = @head
while current
p current.data
current = current.next
end
end

# method to delete the first node found with specified value
def delete(value)
puts "Not implemented"
return if @head == nil

current = @head
@head = current.next if current.data == value
previous = nil

while current.next
if current.data == value
current = current.next
previous.next = current if previous
break
end
previous = current
current = 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
# time complex - constant - cause visiting each node once so depends on linklist size
def reverse
puts "Not implemented"
current = @head
previous = nil
temp = current.next

while current
temp = current.next
current.next = previous
previous = current
current = temp
end

@head = previous
end

## Advanced Exercises
# returns the value at the middle element in the singly linked list

# check input - head is nil return
# if head nex is nil return value at head

# set slow head
# set fast head next

# algo steps
# while fast is not nil
# update slow next
# update falst next
## if fast next is not nil - update fast next

# return value at slow
def find_middle_value
puts "Not implemented"
return if @head == nil
return @head.data if @head.next == nil

slow = @head
fast = @head.next

while fast.next
slow = slow.next
fast = fast.next
fast = fast.next if fast.next
end

return slow.data
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)
puts "Not implemented"
return if @head == nil

current = @head
trailing = nil

i = 0

until i == n
i += 1
current = current.next
end

trailing = @head

while current.next
current = current.next
trailing = trailing.next
end

return trailing.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
puts "Not implemented"
# have a fast and node - when they reach the same position you have a cycle

# two pointers/references, fast and slow, slown and fast start at head
# fast moves twice as fast
# if fast becomes nil - no cycle
# if fast and slow same node - then true cycle
return false if !@head || !@head.next

slow = @head
fast = @head

while fast
slow = slow.next
fast = fast.next

fast = fast.next if fast

return true if fast == slow
end

return false
end

# Creates a cycle in the linked list for testing purposes
Expand All @@ -109,6 +264,7 @@ def create_cycle

## --- END of class definitions --- ##


# Create an object of linked list class
my_linked_list = LinkedList.new()

Expand Down