Add to Tail
by Isai Damier

#=======================================================================
# Author: Isai Damier
# Title: Singly Linked List
# Project: geekviewpoint
# Package: datastructure
#
# Description: A LinkedList is a data structure that allows access
#   to a collection of data using pointers/references. While an
#   array can also be defined as above, LinkedLists and arrays differ
#   in how they are stored in memory and in the operations they
#   allow. Unlike an array that must be stored in a block of memory,
#   the nodes of a LinkedList can be stored anywhere because each
#   node has a reference to the node that succeeds it. Because the
#   nodes are stored so loosely, inserting nodes into a LinkedList
#   is easy; whereas in an array, all the succeeding elements must
#   be shifted. Of course, insertion also means changing the size of
#   the array, which means creating the entire array anew.
#
#   Perhaps the greatest beauty of LinkedList is that it allows
#   accessing an entire sequence of nodes using only one variable:
#   a reference to the first node in the sequence.
#
#   Countless operations can be performed on LinkedLists. Following
#   are a few, ranging from the common to the very interesting.
#======================================================================= 
 #=====================================================================
  # Statement:
  #   Add the given element after the tail of this list
  #   so that this element becomes the new tail.
  #
  # Time Complexity of Solution:
  #   Best = Average = Worst = O(1).
  #
  # Technical Details: The tail is None only if the head is None.
  #   Hence, if the tail is None relay the call to addToHead; else
  #   add the new element to the right of tail and then move the
  #   tail pointer to the rightmost node on the list.
  #===================================================================== 
 import collections
class SinglyLinkedList( object ):

  def __init__( self ):
    self.head , self.tail = None, None

  def addToTail( self, el ):
    if None is self.tail:
      self.addToHead( el )
    else:
      self.tail.next = self.tail = Node( el )

class Node( object ):

  def __init__( self, data, next = None ):
    self.data = data
    self.next = next
import unittest
from algorithms.SinglyLinkedList import SinglyLinkedList
import random

class Test( unittest.TestCase ):
  #=====================================================================
  # Test of addToTail method, of class SinglyLinkedList.
  #=====================================================================
  def testAddToTail( self ):
    tape = [9, 4, 5, 2, 1, 12, 6, 7, 4, 8, 3, 0, 16, 19, 11, 17, 13]
    linkedList = SinglyLinkedList()
    for i in range( len( tape ) ):
      self.assertEquals( i, linkedList.size() )
      linkedList.addToTail( tape[i] )

    ndx = 0
    n = linkedList.head
    while None != n :
      self.assertEquals( tape[ndx], n.data )
      ndx += 1
      n = n.next

    self.assertEquals( len( tape ), ndx )