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  • Your email address will not be published.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

  • The 2014 State of DevOps Report — based on a survey of 9,200+ people in IT operations, software development and technology management roles in 110 countries — reveals: Companies with high-performing IT organizations are twice as likely to exceed their profitability, market share and productivity goals. IT performance improves with DevOps maturity, and strongly correlates with well-known DevOps practices. Job satisfaction is the No. 1 predictor of performance against organizational …

  • Migrating away from Windows Server 2003 is an investment in your organization's future, and there has never been a better time to begin the migration process. Take the next step to transform your datacenter by upgrading your server platform with leading edge Windows Operating Systems and SanDisk flash solutions.

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date