#=======================================================================
# 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 head of this LinkedList.
#
# Time Complexity of Solution:
# O(1).
#=====================================================================
import collections
class SinglyLinkedList( object ):
def __init__( self ):
self.head , self.tail = None, None
def deleteFromHead( self ) :
delt = self.head
if self.head == self.tail:
self.tail = self.head = None # same as self.clear()
else:
self.head = self.head.next
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 deleteFromHead method, of class SinglyLinkedList.
#=====================================================================
def testDeleteFromHead( 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 = 0
while ndx < len( tape ):
n = linkedList.deleteFromHead()
if n != None:
self.assertEquals( tape[ndx], n.data )
else:
self.fail( "linked list has fewer nodes than expected" )
ndx += 1
