Definition: The intrinsic minimum amount of resources, for instance, memory, time, messages, etc., needed to solve a problem or execute an algorithm.

See also complexity class, big-O notation, decision problem, model of computation.

Note: Any measure of execution must implicitly or explicitly refer to some computation model. Usually this is some notion of the limiting factor. For one problem or machine, the number of floating point multiplications may be the limiting factor, while for another, it may be the number of messages passed across a network. Other measures that may be important are compares, item moves, disk accesses, memory used, or elapsed ("wall clock") time.

Author: PEB

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Entry modified 17 December 2004.
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Cite this as:
Paul E. Black, "complexity", in Dictionary of Algorithms and Data Structures [online], Paul E. Black, ed. 17 December 2004. (accessed TODAY) Available from: