Clarification of Exercise 9.2-4

A model of the situation described in the problem is that of an array of records identified by integral key values. (For instance, student records keyed by CRN of the course a student takes at a given time.) Since the statement of the problem requires outputting records of the array in a non-increasing order of (integer) key values, simple counting records with identical keys may not suffice, as the identity of the records themselves would then be lost. The hint indicates a solution by linking records with the same key together using no more than a constant amount of extra memory space. (Requiring a new pointer field for each record would not fit the bill.)