title: Simple and efficient container in C++ with characteristics of map and list containers
body: <p>I'm looking for a C++ container that will enjoy both map container and list container benefits.</p>
  
  <p><strong>map</strong> container advantages I would like to maintain:</p>
  
  <ul>
  <li>O(log(n)) access</li>
  <li>operator[] ease of use</li>
  <li>sparse nature</li>
  </ul>
  
  <p><strong>list</strong> container advantages I would like to maintain:</p>
  
  <ul>
  <li>having an order between the items</li>
  <li>being able to traverse the list easily <strong>UPDATE: by a sorting order based on the key or value</strong></li>
  </ul>
  
  <p>A simple example application would be to hold a list of certain valid dates (business dates, holidays, some other set of important dates...), once given a specific date, you could find it immediately "map style" and then find the next valid date "list style". </p>