title: Given sorted vector find transition from negative to positive
body: <p>Given a sorted <code>std::vector&lt;int&gt;</code>, I would like, using C++11-STD functions, to  find the index where the elements transition from negative to positive.</p>
  
  <p>I am aware that I can implement this using a binary search but I am interested if there is any function in the standard library, similar to the unary<code>find_if</code>, which would facilitate this search (maybe in connection with the right lambda expression).</p>