Mastering the C++17 STL

Rotation and permutation

Remember our code from Swapping, reversing, and partitioning to reverse the order of words in a sentence? When the "sentence" contains only two words, there is another way to look at the reversal: you could consider it a cyclic rotation of the elements in the underlying range. std::rotate(a,mid,b) rotates the elements of the range [a,b) so that the element formerly addressed by mid is now at a (and returns an iterator pointing to the element whose value was formerly at a):

    template<class FwdIt>    FwdIt rotate(FwdIt a, FwdIt mid, FwdIt b)    {      auto result = a + (b - mid);      // First, reverse the whole range.      std::reverse(a, b);      // Next, un-reverse each individual segment.      std::reverse(a, result); std::reverse(result, b); ...