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## 0.5.2 Permutations

Imagine we have a collection of n distinct objects. There are n! ways to order these objects; that is, we can form n! different arrangements of these n objects. This is true because any such arrangement will consist of n items, no matter which happens to be first. To choose the first object in a particular arrangement we have n options. However, to choose the second object after already having placed the first, we are left with one less choice. The first object is fixed at this point. Thus, we have (n-1) alternatives. As we place more and more objects we have less and less choices of objects to place. The summation below follows from this discussion:

This is the same as n!.

This section presents an algorithm for calculating all possible permutations (that is, not just the number of permutations but the actual permutated data) given the number of distinct data items to be arranged.

Scott Gasch
1999-07-09