#=======================================================================
# 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:
# Retrieve and remove the tail of this LinkedList.
#
# Time Complexity of Solution:
# O(n).
#
# Technical Details: Because the element preceding the self.tail must
# now become the new self.tail, this is a O(n) operation.
#
#=====================================================================
import collections
class SinglyLinkedList( object ):
def __init__( self ):
self.head , self.tail = None, None
def deleteFromTail( self ) :
delt = self.tail
if self.head == self.tail:
self.head = self.tail = None # same as self.clear()
else:
p = self.head
while p.next != self.tail:
p = p.next
p.next = None
self.tail = p
return delt
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 deleteFromTail method, of class SinglyLinkedList.
#=====================================================================
def testDeleteFromTail( self ):
tape = [9, 4, 5, 2, 1, 12, 6, 7, 4, 8, 3, 0, 16, 19, 11]
linkedList = SinglyLinkedList()
self.assertIsNone( linkedList.deleteFromHead() )
for i in range( len( tape ) ):
linkedList.addToTail( tape[i] )
ndx = len( tape ) - 1
while ndx >= 0:
self.assertEquals( tape[ndx], linkedList.deleteFromTail().data )
ndx -= 1
