/* This is standard modern C++ random number generation.
       It means, using the random generator "engine", return 
       a number according to distribution "dist". In this
       "dist" is a uniform distribution from "i" to "max-min".
       "auto" is the new way to type variables in C++: it
       infers the type of the variable from the type of the
       expression */
    22: auto index = dist(engine);

    /* The following lines are a bit more complex, as they
       contain a nested expression. Let us focus on the inner
       expression:
           (index < size ) ? array[index]
              : map.insert({index, min + index}).first->second

       This is in the form:
           test-expr ? when-true-expr
              : when-false-expr

       This expression is a ternary condition. What it means
       is that the expression before the question mark is
       computed (index < size), and if it evaluates to true,
       the overall expression will resolve to the result of
       the expression between the question mark and the colon,
       otherwise it resolves to what is after the colon.

       Here, it means that if "index" is smaller than "size",
       use "array[index]", otherwise insert a new entry in the
       map, with key "index" and value "min+index", then reuse
       the result of the operation by accessing member "second"
       of the member "first". I am not familiar with STL maps;
       here is an explanation of the map::insert method from
       cplusplus.com:

           The single element versions (1) return a pair, with
           its member pair::first set to an iterator pointing 
           to either the newly inserted element or to the 
           element with an equivalent key in the map. The 
           pair::second element in the pair is set to true if 
           a new element was inserted or false if an equivalent
           key already existed.
    */

    23: std::swap(array[i], index < size
    24:                         ? array[index]
    25:                         : map.insert({index, min + index}).first->second);

    /* Then, the std::swap operation simply swaps the two indicated
       values in the array. */