First pass at in-place interleave

void deinterleave(int *a, int len)
{
    for (int i = 0; i < len/2; i++)
    {
        // move a left int into place
        for (int j = i * 2; // initial position
             j > i;         // final position
             j --)
        {
            int t = a[j-1];
            a[j-1] = a[j];
            a[j] = t;
        }
    }
}

void interleave(int *a, int len)
{
    for (int i = len/2-1; i > 0; i--)
    {
        // move a left int into place
        for (int j = i; // initial position
             j < i*2;   // final position
             j ++)
        {
            int t = a[j+1];
            a[j+1] = a[j];
            a[j] = t;
        }
    }
}