An unordered_set is an unordered collection of zero or more unique C++ data values of a particular type. To use unordered_sets, you import unordered_set from the Standard template library with #include <unorderd_set>.
Unordered_sets allow for fast retrieval of individual elements based on their value. In an unordered_set, the value of an element is at the same time its key, that identifies it uniquely. Keys are immutable, therefore, the elements in an unordered_set cannot be modified once in the container - However, they can be inserted and removed.
Unordered sets do not allow duplicates and are initialized using comma-delimited values enclosed in curly braces. The collection can be assigned to a variable as shown below.
Unordered sets support a number of methods that should be familiar to those who have worked with sets in a mathematics setting. Table 5.6.1 provides a summary. Examples of their use follow.
the find method used for a conditional in Checker compares each item in the set with the given parameter until there is a match. the set.find(letter) == set.end() section means that if find cannot find the letter before reaching the end of the set, then letter is not contained in the set.
