#=======================================================================
# 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.
#=======================================================================
#=====================================================================
# Time Complexity of Solution:
# O(n).
#
# Description: Delete all duplicates from this list, such that
# iabcdeafgdc becomes iabcdefg
#
# Technical Details: The easiest way to remove duplicates from
# a collection tends to be with a hashmap. Here is a process:
# 0] traverse the list, sending data to a linked hashmap, which
# discards duplicates. (Do deleteFromHead if acceptable)
# 1] empty the linked hashmap into a new linked list.
# Time Complexity is O(n) Space Complexity is O(n)
#
# Note: I code to python 2.7 because that's what most people are
# using and it's harmless for fundamentals. But you don't need
# ordereddict for your linked-hashmap if you have python 3.x
#=====================================================================
import collections
class SinglyLinkedList( object ):
def __init__( self ):
self.head , self.tail = None, None
def deleteDuplicates( self ) : # min, max, avg, sum, size
noDups = collections.OrderedDict()
t = self.deleteFromHead()
while ( None != t ): # if(!noDups.containsKey(t.data)): not necessary
noDups[ t.data] = 1
t = self.deleteFromHead()
# reconstruct linkedlist
for k in noDups.keys():
self.addToTail( k )
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 deleteDuplicates method, of class SinglyLinkedList.
#=====================================================================
def testDeleteDuplicates( self ):
tape = [2, 19, 11, 5, 17, 11, 1, 17, 2, 11]
linkedList = SinglyLinkedList()
for i in range( len( tape ) ):
linkedList.addToTail( tape[i] )
exp = [2, 19, 11, 5, 17, 1]
linkedList.deleteDuplicates()
self.assertEquals( exp, linkedList.toArray() )