#=======================================================================
# 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 )
