In-place interleaving of the two halves of a string

Question

Given a string of even size, say:

abcdef123456

How would I interleave the two halves, such that the same string would become

Answer 1

Alright, here's a rough draft. You say you don't just want an algorithm, but you are taking hints, so consider this algorithm a hint:

Length is N.

k = N/2 - 1.

1) Start in the middle, and shift (by successive swapping of neighboring pair elements) the element at position N/2 k places to the left (1st time: '1' goes to position 1).

2) --k. Is k==0? Quit.

3) Shift (by swapping) the element at N/2 (1st time:'f' goes to position N-1) k places to the right.

4) --k.

Edit: The above algorithm is correct, as the code below shows. Actually proving that it's correct is waaay beyond my capabilities, fun little question though.

#include 
#include 

int main(void)
{
    std::string s("abcdefghij1234567890");
    int N = s.size();
    int k = N/2 - 1;
    while (true)
    {

        for (int j=0; j