#=======================================================================
# 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.
#=======================================================================
#=====================================================================
# Description: Retrieve and remove the specified element.
#
# One of the drawbacks of LinkedList is that
# it allows no random access. Therefore deleting a random
# element is a O(n) process because the list must first be
# traversed to find the node containing the element.
#
# Technical Details:
# 0] If el is the self.head, simply delete from self.head and
# return: O(1).
# 1] If el is the self.tail, simply delete from self.tail and
# return: O(1).
# 2] Otherwise, find the node containing el, and its parent.
# 3] If said node is not None, give its parent custody of its child.
# 4] Return the node.
#=====================================================================
import collections
class SinglyLinkedList( object ):
def __init__( self ):
self.head , self.tail = None, None
def delete( self, el ):
if el == self.head.data: # O(1)
return self.deleteFromHead()
if el == self.tail.data: # O(1)
return self.deleteFromTail()
parent , curr = None, self.head
while None != curr and el != curr.data:
parent = curr
curr = curr.next
if None != curr:
parent.next = curr.next
return curr
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 delete method, of class SinglyLinkedList.
#=====================================================================
def testDelete_int( self ):
tape = [9, 4, 5, 2, 1, 12, 6, 7, 4, 8, 3, 0, 16, 19, 11]
linkedList = SinglyLinkedList()
for i in range( len( tape ) ):
linkedList.addToTail( tape[i] )
self.assertEquals( tape[0], linkedList.delete( tape[0] ).data )
self.assertEquals( tape[5], linkedList.delete( tape[5] ).data )
last = len( tape ) - 1
self.assertEquals( tape[last], linkedList.delete( tape[last] ).data )
expected = [4, 5, 2, 1, 6, 7, 4, 8, 3, 0, 16, 19]
self.assertEquals( None, linkedList.delete( 51 ) )
self.assertEquals( expected, linkedList.toArray() )