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Posted 31 Aug 2009

# NLineDiffConsole: A Console diff Implementation for Text Files

, 31 Aug 2009
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An entry for the Lean and Mean competition

## Introduction

This article is an entry for the Lean and Mean competition, which ran on The Code Project during August 2009.

This is a console version of my previous entry. As such, it also uses the diff algorithm with the linear space refinement. I have included the original paper in the downloads. In this version, I have halved the memory requirements, but the algorithm is the same.

Correction: According to Wikipedia, the algorithm was written by Douglas McIlroy in the early 70's while Eugene W. Myers only described it in his paper. Apologies.

## Background

If N = number of lines in the first file, M = number of lines in the other file and D = number of different lines, then the diff algorithm is O( (N+M) D ) in time and O( N+M ) in space.

This is far better than the LCS algorithm, which is O( N * M ) in both time and space. For the test files N = 1784, M = 1789 and D = 19. So in this case, the complexity of the LCS algorithm is several orders of magnitude fatter and slower than the diff algorithm.

I have to repeat my appreciation of McIlroy's algorithm. The more I have learned about it, the more impressed I have become. I certainly couldn't invent anything better!

## Using the Code

The demo is a console application that uses the diff implementation, which is in a separate assembly. The demo takes two file paths as arguments. It reads the files, calculates the diff and displays the results and some timing measurements. There is a `#define` in program.cs that optionally measures the change in `Process.PeakWorkingSet64`.

## Results

The screenshot above shows the timing results for a typical run. Not including the JIT compilation gives times of about 5.5 ms. Including it gives overall times of about 32 ms.

The main arrays used by the algorithm are now a bit under 30 KB, so the calculated memory use is 420 KB plus change.

Other entries measure the change in `Process.PeakWorkingSet64`, so I will do the same. The measurements vary dramatically, but values of 600 - 700 KB are common.

## History

• 2009 08 31: First edition

## About the Author

 United Kingdom

I built my first computer, a Sinclair ZX80, on my 11th birthday in 1980.
In 1992, I completed my Computer Science degree and built my first PC.
I discovered C# and .NET 1.0 Beta 1 in late 2000 and loved them immediately.
I have been writing concurrent software professionally, using multi-processor machines, since 1995.

In real life, I have spent 3 years travelling abroad,
I have held a UK Private Pilots Licence for 20 years,
and I am a PADI Divemaster.

I now live near idyllic Bournemouth in England.

I can work 'virtually' anywhere!

 Pro

## Comments and Discussions

 First Prev Next
 yours faster sajamp30-Oct-14 5:48 sajamp 30-Oct-14 5:48
 Great. Luc Pattyn31-Aug-09 16:02 Luc Pattyn 31-Aug-09 16:02
 Re: Great. Nick Butler31-Aug-09 23:47 Nick Butler 31-Aug-09 23:47
 Re: Great. Luc Pattyn31-Aug-09 23:57 Luc Pattyn 31-Aug-09 23:57
 Re: Great. Chris Maunder4-Sep-09 9:10 Chris Maunder 4-Sep-09 9:10
 Luc Pattyn wrote:All that remains to be said now is: May Chris have a hard job figuring it all out You have your wish. This is not easy! (but have no fear - I think there will be multiple winners based on different features we like best) cheers, Chris Maunder The Code Project Co-founder Microsoft C++ MVP
 Last Visit: 31-Dec-99 18:00     Last Update: 26-Jun-17 14:30 Refresh 1

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