Programmers waste enormous amounts of time thinking about, or worrying about, the speed of noncritical parts of their programs, and these attempts at efficiency actually have a strong negative impact when debugging and maintenance are considered. We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. Yet we should not pass up our opportunities in that critical 3%.
--- Donald Knuth, "Structured Programming with go to Statements" (http://dl.acm.org/citation.cfm?id=356640)Rule 1. You can't tell where a program is going to spend its time. Bottlenecks occur in surprising places, so don't try to second guess and put in a speed hack until you've proven that's where the bottleneck is.
Rule 2. Measure. Don't tune for speed until you've measured, and even then don't unless one part of the code overwhelms the rest.
Rule 3. Fancy Algorithms are slow when n is small, and n is usually small. Fancy algorithms have big constants. Until you know that n is frequently going to be big, don't get fancy. (Even if n does get big, use Rule 2 first.) For example, binary trees are always faster than splay trees for workaday problems.
Rule 4. Fancy algorithms are buggier than simple ones, and they're much harder to implement. Use simple algorithms as well as simple data structures.
The following data structures are a complete list for almost all practical programs:
array
linked list
hash table
binary tree
Of course, you must also be prepared to collect these into compound data structures. For instance, a symbol table might be implemented as a hash table containing linked lists of arrays of characters.
Rule 5. Data dominates. If you've chosen the right data structures and organized things well, the algorithms will almost always be selfevident. Data structures, not algorithms, are central to Programming. (See Brooks p. 102.)
Rule 6. There is no Rule 6.
--- Rob Pike, "Notes on Programming in C" (http://www.lysator.liu.se/c/pikestyle.html)
Representation Is the Essence of Programming - Very often, strategic breakthroughs will come from redoing the representation of data or tables. The programmer at wit's end for lack of space can often do best by disentangling from code, rearing back, and contemplating the data.
--- Frederick P. Brooks, Jr, "The Mythical Man-Month" (http://javatroopers.com/Mythical_Man_Month.html)
