Question

I have two vectors: a vector and index vector. How can I make the vector be arranged by the indexes vector? Like:

Indexes                5 0 2 1 3 4
Values                 a b c d e f
Values after operation b d c e f a

The indexes vector will always contain the range [0, n) and each index only once.
I need this operation to be done in place because the code is going to be run on a device with low memory.
How can I do this in c++? I can use c++11

Answer 1

std::vector<int>  indices = { 5,   0,   2,   1,   3,   4};
std::vector<char> values  = {'a', 'b', 'c', 'd', 'e', 'f'};

for(size_t n = 0; n < indices.size(); ++n)
{
    while(indices[n] != n)
    {
        std::swap(values[n],  values[indices[n]]);
        std::swap(indices[n], indices[indices[n]]);
    }
}

EDIT:

I think this should be O(n), anyone disagree?