There is usually more than one way to solve a problem and if efficiency is a concern, you should first and foremost focus on the high-level optimizations by choosing the right algorithms and data structures. A useful way of evaluating and comparing algorithms is by analyzing their asymptotic computational complexity—that is, analyzing how the running time or memory consumption grows when the size of the input increases. In addition, the C++ Standard Template Library (STL) specifies the asymptotic complexity for all containers and algorithms, which means that a basic understanding of this topic is a must if you are using STL. If you already have a good understanding of algorithm complexity and the big O notation, you can safely skip this section.

Let's start off with an example. Suppose we want to write an algorithm that returns...