## brute force

**brute force** /adj./ Describes a primitive programming style,
one in which the programmer relies on the computer's processing
power instead of using his or her own intelligence to simplify the
problem, often ignoring problems of scale and applying naive
methods suited to small problems directly to large ones. The term
can also be used in reference to programming style: brute-force
programs are written in a heavyhanded, tedious way, full of
repetition and devoid of any elegance or useful abstraction (see
also brute force and ignorance).
The canonical example of a brute-force algorithm is associated
with the `traveling salesman problem' (TSP), a classical
NP-hard problem: Suppose a person is in, say, Boston, and
wishes to drive to N other cities. In what order should the
cities be visited in order to minimize the distance travelled? The
brute-force method is to simply generate all possible routes and
compare the distances; while guaranteed to work and simple to
implement, this algorithm is clearly very stupid in that it
considers even obviously absurd routes (like going from Boston to
Houston via San Francisco and New York, in that order). For very
small N it works well, but it rapidly becomes absurdly
inefficient when N increases (for N = 15, there are
already 1,307,674,368,000 possible routes to consider, and for
N = 1000 -- well, see bignum). Sometimes,
unfortunately, there is no better general solution than brute
force. See also NP-.

A more simple-minded example of brute-force programming is finding
the smallest number in a large list by first using an existing
program to sort the list in ascending order, and then picking the
first number off the front.

Whether brute-force programming should actually be considered
stupid or not depends on the context; if the problem is not
terribly big, the extra CPU time spent on a brute-force solution
may cost less than the programmer time it would take to develop a
more `intelligent' algorithm. Additionally, a more intelligent
algorithm may imply more long-term complexity cost and bug-chasing
than are justified by the speed improvement.

Ken Thompson, co-inventor of Unix, is reported to have uttered the
epigram "When in doubt, use brute force". He probably intended
this as a ha ha only serious, but the original Unix kernel's
preference for simple, robust, and portable algorithms over
brittle `smart' ones does seem to have been a significant
factor in the success of that OS. Like so many other tradeoffs in
software design, the choice between brute force and complex,
finely-tuned cleverness is often a difficult one that requires both
engineering savvy and delicate esthetic judgment.

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