programming-for-dummies

Chapter 3: String Searching
In This Chapter
Searching text sequentially
Searching by using regular expressions
Searching strings phonetically
Searching for data is one of the most common functions in writing a computer
program. Most searching algorithms focus on searching a list of
values, such as numbers or names. However, there’s another specialized type
of searching, which involves searching text.
Searching text poses unique problems. Although you can treat text as one
long list of characters, you aren’t necessarily searching for a discrete value,
like the number 21 or the last name Smith. Instead, you may need to search
a long list of text for a specific word or phrase, such as ant or cat food.
Not only do you need to find a specific word or phrase, but you also may
need to find that same word or phrase multiple times. Because of these differences,
computer scientists have created a variety of searching algorithms
specifically tailored for searching text.
Computers only recognize and manipulate numbers, so every computer represents
characters as a universally recognized numeric code. Two common
numeric codes include the American Standard Code for Information Interchange
(ASCII) and Unicode. ASCII contains 256 codes that represent mostly Western
characters whereas Unicode contains thousands of codes that represent languages
as diverse as Arabic, Chinese, and Cyrillic. When searching for text,
computers actually search for numeric codes that represent specific text, so
text searching is ultimately about number searching.
One of the most popular uses for text searching algorithms involves a field
called bioinformatics, which combines molecular biology with computer programming.
The basic idea is to use long text strings, such as gcacgtaag, to
represent a DNA structure and then search for a specific string within that
DNA structure (such as cgt) to look for matches that could indicate how a
particular drug could interact with the DNA of a virus to neutralize it.