#=======================================================================
# 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 element el after node x
#
# Time Complexity of Solution:
# Best = O(1) Worst = O(n).
#
# Description:
#
# Technical Details: We simply need to find node x on the list
# and then attach the new node containing el to said node, which
# we represent as tmp. If x is not found, then el is not added.
# instead of having a traversal algorithm all the time, we treat the
# possibility of x being the tail of the list as a special case
# where the problem could be solved in O(1)
#=====================================================================
import collections
class SinglyLinkedList( object ):
def __init__( self ):
self.head , self.tail = None, None
def addAfter( self, el, n ):
if None == self.tail or n.data == self.tail.data:
self.addToTail( el )
else:
tmp = self.head
while None != tmp and n.data != tmp.data:
tmp = tmp.next
if None != tmp:
tmp.next = Node( el, tmp.next )
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 addAfter method, of class SinglyLinkedList.
#=====================================================================
def testAddAfter( 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] )
value = 51
linkedList.addAfter( value, linkedList.find( 7 ) )
expected = [9, 4, 5, 2, 1, 12, 6, 7, 51, 4, 8, 3, 0, 16, 19, 11]
self.assertEquals( expected, linkedList.toArray() )
