Home Contact Shop Notes Questions Programming Links Dictionary Coursework FORUM Tutors
 Recommended Amazon Searches: Computer Science | Computing | Computer Systems | Database | Computing Revision

Notes > Foundations of Computing > Permutations and Combinations

Permutations

A permutation is a linear arrangement of a group of items. Each unique way of ordering the items of a group is known as a permutation. The number of ways to arrange a group of n items is n! (factorial of n). This means n x n-1 x n-2 x ... x 1.

The number of permutations (of length r) that can be made from a set of n items is:

n! / (n-r)!
This has the simplified notation: nPr

Combinations

A combination is a set containing a certain number of objects that have been selected from another set. In combinations, the order of the elements does not matter.

The number of combinations (of length r) that can be made from a set of n items is:

n! / ((n-r)! r!)
This has the simplified notation: nCr

Search for "Permutations and Combinations" on: Google | Kelkoo | Amazon | eBay (UK) | eBay (US)

Search for "Permutations and Combinations" on the rest of Computing Students: Permutations and Combinations

 Home | Contact | Shop | Notes | Questions | Programming | Links | Dictionary | Coursework | Tutors Sponsored Links: Affiliate Program Articles | Computer Science Definitions | CS Degree Notes
 Copyright © 2005-2009 ComputingStudents.com This site is to be used in accordance with the ComputingStudents.com User Agreement