C++ In a Nutshell

Name

prev_permutation function template — Generates previous permutation

Synopsis

template<typename BidiIter>
  bool prev_permutation(BidiIter first, BidiIter last);
template<typename BidiIter, typename Compare>
  bool prev_permutation(BidiIter first, BidiIter last, Compare comp);

The prev_permutation function template rearranges the contents of the range [first, last) to the previous permutation, assuming that there is a set of lexicographically ordered permutations. The return value is true if the previous permutation is generated, or false if the range is at the first permutation, in which case the function cycles and generates the last permutation (that is, with all elements in descending order).

Figure 13-9 (under next_permutation) shows all the permutations, in order, for a sequence. The prev_permutation function swaps elements to form the previous permutation. For example, if the input is permutation 3, the result is permutation 2. If the input is permutation 1, the result is permutation 6, and prev_permutation returns false.

Technical Notes

Complexity is linear: at most (last - first) / 2 swaps are performed.

See Also

lexicographical_compare function template, next_permutation function template, swap function template