https://stackoverflow.com/a/10758845/12509349

The top answer does a very nice job of breaking down many different ways to print out the contents of a vector, which is very very similar to the problem in the Kata. While reading this, note that all the different techniques are supposed to do the same thing.

first and second are key terms in C++ which reference the first and second items in a pair. These are also used for the key and value of a map (dictionary).