個人的に気に入っているのは、言語が連想配列をもつPerlのせいでしょうか、アルゴリズムの抽象性がよく浮き出されている点です。特にいわゆる抽象データ型の扱いは見事です。れがＣ等の言語だと、アルゴリズムの本質とは無関係な部分、例えば配列の添え字の扱いやら、ポインタの扱いがコードの多くを占めてしまい、本質への見通しが悪くなります。もちろん、P... 続きを読む ›
This is only a problem early on though because as the book progresses, the authors stop describing the code examples! In fact, I found myself trying to figure out what the text was doing in the chapters since all of the concepts were explained in code (without full explanations in the text). <this is a minor exaggeration>
In addition, I found the unrelated annecdotes and allusions and obscure literary quotes a further distraction. I'm sure there is a certain academic audience that would appreciate this, but I hate having to look up words only to find out I didn't really need to look them up ;-).
Some other things I disliked were the absence of hashes in the data structures section (perl has built in hashes, so you'd think a discussion on what a hash is, and hashing algorithms would be included in a perl algorithms book), and the description of algorithm analysis was too short.
On the up side, the sorting and searching sections are very thorough (the perl code implementing them, not the text explaining the code), as are the other sections. If its perl your after, this book has some of the best perl code in print (save for Joseph Hall's "Effective Perl").
In summary, if you already understand these topics, then this book will show you some excellent perl code to implement them. If you do not understand the data structures and algorithms already, I don't think this book is going to make them crystal clear (though the authors are good about referring the reader to other sources).
4 camels for the high quality perl code and thoroughness, but it could have been 5 if the authors followed through with the type of supporting text that Hall did in EP.
The first few chapters outline PERL data structures, with the built-in data structures discussed, along with a discussion of how to create new ones. The dynamic nature of arrays in PERL is emphasized, and this is a feature that sets PERL way above other languages, such as C and C++. Linked lists are given a detailed treatment along with garbage collection in PERL. The authors are careful to point out that reference counting in PERL will fail when one is dealing with a circle of reference values.
A discussion of sorting follows, with radix and hybrid sorts being the most useful of the algorithms discussed. The authors give a useful comparison study of the running time of the sorting algorithms. This is followed by a discussion of searching algorithms, which unfortunately omits any details of dynamic programming, which is useful in applying PERL to areas such as computational biology.
The authors give a very interesting treatment of how to do set operations using PERL in the next chapter. They did not treat the case of fuzzy sets in detail though, unfortunately.
Matrix algorithms are discussed next, with the PERL modules MatrixRead and PDL integrated into the discussion. I have only used PDL and its graphic library PGPLOT and have had varying degress of success with it. PERL still has a long way to go before it is accepted as a language suitable for numerical computations.
Graph algorithms are the subject of the next chapter. The most useful section is the one on minimum spanning trees, so useful in network routing algorithms.
This is followed by a thorough discussion of string algorithms in Chapter 9. These algorithms are extremely important in current applications, such as string matching and alignment in computational biology. That the authors give the source code for the algorithms is extremely helpful to those who need to apply these algorithms.
The authors return to geometric algorithms in the next chapter, with only elementary ones being discussed, with brief overviews of PERL graphics modules available.
Number systems and numerical precision are taken up in the next chapter, with 32 bit precision implemented in the discussion. The authors do however discuss how large number arithmetic can be implemented in PERL via the BigFloat and BigInt modules. This is followed by modular arithmetic and number theory , with PERL code given for the Miller-Rabin primality test. This chapter is very short, but it sets up the next chapter on cryptography, which begins with a discussion of passwords, with a PERL program given that checks valid passwords. Then, interestingly, a PERL 1-liner is given for cracking a password list. The discussion on passwords should be of interest to individuals first entering the field of computer security. This is followed by a fairly complete elaboration on authentication and checksums. Encryption of data is discussed in the next section, along with a brief mention of the AES, which at the time of publication of this book, was not settled. The RSA algorithm is discussed also, with a 3-line PERL code given for it, along with a more instructive version later. Only one section on steganography is included, and since this is a subject of intense research with useful applications, this is somewhat disappointing.
The last three chapters covers probability and statistics and numerical analysis, and given the growing use of PDL in astrophysics and other areas of science, this is a fitting way to end the book. PERL code is given for the most popular probability distributions, and also for some of the standard statistical tests. Only some rudimentary algorithms are given for calculus and data interpolation, but the discussion should prepare the reader for more advanced reading in numerical algorithms using PERL and the use of PDL.
When I heard that O'Reilly was publishing a book on Algorithms in Perl I couldn't wait to get my hands on it. Well last month I did and it was great!
The clearly written text contains the usual light, easy-reading tone and occasional humorous elements found in most O'Reilly books. The authors include plenty of pictures and diagrams for those who learn visually (rather then by reciting words out loud). The Perl code within is concise, with comments when necessary, and makes use of the objects when possible. If you plan to read this book you should know Perl because the more advanced level of the code could cause problems for the non-Perl or beginning Perl Programmer. However, to a Perl programmer who is comfortable with the language the code reads clean and understandably - sometimes it's even more clear then pseudocode.
The text covers a broad range of topics (with varying levels of complexity). When I was reading I recalled things I learned in college classes such as: Data Structures, Algorithm Analysis, Discrete Math, Calculous, Linear Algebra, Statistics, Compiler Design, Signal Processing, and even some good old fashion high school geometry. I found this extremely helpful because the broad nature of the book doesn't allow the authors to cover a topic in great detail. They do review each topic area giving the proper terminology used along with background of how the field developed.
Within the different chapters the authors present various code segments. For some segments the authors have written there own code to implement the algorithms. In other cases, as is Perl custom, the authors have searched CPAN for the modules that implement the algorithm. Then the example code demonstrates the proper use of that module.
One of the features I really enjoyed is that each chapter can stand on its own as a nice review of the algorithms in that section. (In cases where they build on other sections you are reminded where to go and read.) Another great feature the authors include is the references - all the web sites and books you'll need are listed in Appendix A, by topic area.
The only thing I really felt was missing was a discussion on some AI topics such as Neural Networks and Genetic Programming. (If you're interesting Neural Networks in general check out The Linux Journal July 1999 p 44. For Genetic Programming in Perl check out The Perl Journal Fall 1999 p 34)
Overall, this book explains methods of implementing Algorithms with Perl blending custom techniques with resources available (CPAN) in a "learn by example" approach. It contains 16 great chapters of background, theory, sample code, diagrams, and discussion. It has a good Appendix A (for additional info on algorithms) and a useful ASCII table in Appendix B. If you want to learn good ways to implement specific Algorithms with Perl - Read this book!