C++ String Interview Question

Question

I was recently in a C++ technical interview, where I was given a bit of simple string manipulation code, which is intended to take a string and return a string that is comprised

Answer 1

// compiled with cl /Ox first_last_n.cpp /W4 /EHsc

inline void
first_last_n2(string::size_type n, const std::string &s, string &out)  // method 2
{
  // check against degenerate input
  assert(n > 0);
  assert(n <= s.size());

  out.reserve(2*n);
  out.assign(s, 0, n);
  out.append(s, s.size()-n, n);
}

Times:

method 1:  // original method
2.281
method 2:  // my method
0.687
method 3:  // your code.
0.782

Note: Timing specifically tests "long" strings. I.e. those where short string optimization is not used. (My strings were 100 length).