The.Algorithm.Design.Manual.Springer-Verlag.1998

Expressing Algorithms
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Expressing Algorithms
Describing algorithms requires a notation for expressing a sequence of steps to be performed. The three
most common options are (1) English, (2) pseudocode, or (3) a real programming language. Pseudocode
is perhaps the most mysterious of the bunch, but it is best defined as a programming language that never
complains about syntax errors. All three methods can be useful in certain circumstances, since there is a
natural tradeoff between greater ease of expression and precision. English is the most natural but least
precise language, while C and Pascal are precise but difficult to write and understand. Pseudocode is
useful because it is a happy medium.
The correct choice of which notation is best depends upon which of the three methods you are most
comfortable with. I prefer to describe the ideas of an algorithm in English, moving onto a more formal,
programming-language-like pseudocode to clarify sufficiently tricky details of the algorithm. A common
mistake among my students is to use pseudocode to take an ill-defined idea and dress it up so that it looks
more formal. In the real world, you only fool yourself when you pull this kind of stunt.
The implementation complexity of an algorithm is usually why the fastest algorithm known for a problem
may not be the most appropriate for a given application. An algorithm's implementation complexity is
often a function of how it has been described. Fast algorithms often make use of very complicated data
structures, or use other complicated algorithms as subroutines. Turning these algorithms into programs
requires building implementations of every substructure. Each catalog entry in Section points out
available implementations of algorithms to solve the given problem. Hopefully, these can be used as
building blocks to reduce the implementation complexity of algorithms that use them, thus making more
complicated algorithms worthy of consideration in practice.
Next: Keeping Score Up: Introduction to Algorithms Previous: Efficiency
Algorithms
Mon Jun 2 23:33:50 EDT 1997
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