Algorithm for Detecting Duplicate/Previously Encountered Strings

Environment: Straight C++

Overview

A challenge I've seen pop up often while writing search tools is the ability to verify that your code is not traversing the same source multiple times. A spider traversing the web, for example, would never wish to traverse the same URL twice in a session - to do so would merely allow circular loops and endless headaches.

To address this issue, I wrote an N-tree based search algorithm that breaks strings down by their leading characters. Identical portions are 'clipped' and stored in a single node, with the remainder of the string in similarly divided child nodes.

Example

Inserting the following text:
1234
12345
123456
1234567
www.another.site.org/index.html
www.site.org/index.html
www.test.com/index2.html
www.test.com/index.html
www.test.com

Results in this data structure
+-NULL
  +-1234
    +-NULL
    +-5
      +-NULL
      +-6
        +-NULL
        +-7
  +-www.
    +-another.site.org/index.html
    +-site.org/index.html
    +-test.com
     +-NULL
     +-/index
        +-2.html
        +-.html

The advantage to this approach over typical linear searches is two-fold.

  1. The memory overhead can be reduced as redundant text is partially eliminated
  2. Since the tree is ordered, a search can be performed in O(Log(N)) time (someone please correct me if my estimate of this algorithm is incorrect!)

On a 600 MHz PIII system, the following benchmarks were obtained for inserting 3000 random strings of length 0-254 characters into an array that already contains 12,000 strings.
Linear search: 2.7 seconds
StringTree: 0.02 seconds
A reasonable improvement!

The attached code implements the algorithm as a CStringTree class, and provides a test / performance driver to demo the code.

Updates

Changes to current source (zip file below):

  • Fixed several small memory leaks
  • Added significant functionality for searching and File / CStringArray I/O
  • Compiler defs for Borland compilers
  • String counting and data association per node

Downloads

Download demo and source code - 12 Kb


Comments

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • On-demand Event Event Date: December 18, 2014 The Internet of Things (IoT) incorporates physical devices into business processes using predictive analytics. While it relies heavily on existing Internet technologies, it differs by including physical devices, specialized protocols, physical analytics, and a unique partner network. To capture the real business value of IoT, the industry must move beyond customized projects to general patterns and platforms. Check out this webcast and join industry experts as …

  • On-demand Event Event Date: October 29, 2014 It's well understood how critical version control is for code. However, its importance to DevOps isn't always recognized. The 2014 DevOps Survey of Practice shows that one of the key predictors of DevOps success is putting all production environment artifacts into version control. In this webcast, Gene Kim discusses these survey findings and shares woeful tales of artifact management gone wrong! Gene also shares examples of how high-performing DevOps …

Most Popular Programming Stories

More for Developers

RSS Feeds