题记 似乎所有的领域 发展到最后 都会变成哲学 —男哥
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.)
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.
Rule 5. Data dominates. If you’ve chosen the right data structures and
organized things well, the algorithms will almost always be self-evident. Data
structures, not algorithms, are central to programming. 
Rule 6. There is no Rule 6