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vector<int> has both vector<int>::size_type and vector<int>::difference_type. It seems unnecessary for both to exist since size_type is guaranteed to be able to hold a value as large as the maximum number of elements that a vector<int> may contain on a given system, and, in any valid use case, difference_type should necessarily be less than or equal to the maximum number of elements i.e. the distance between two elements in a sequential container will never be larger than the maximum number of elements that sequential container can contain. Could someone provide an example where there's a useful distinction between the two?
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std::deque (double-ended queue) is an indexed sequence container that allows fast insertion and deletion at both its beginning and its end.
A Random Access Container is a Reversible Container whose iterator type is a Random Access Iterator. It provides amortized constant time access to arbitrary elements.
Sets are the containers in C++ STL for storing elements in a given order. The elements of a set must be unique. The value itself can identify each element in a set, i.e., they act as keys themselves.
container::difference_type exists because for some sequence containers you can subtract iterators. That subtraction can result in a negative number. You can't use container::size_type for that result as it is unsigned so you will never have a negative value. So we have container::difference_type which is a signed integer that is the difference_type of the iterator of the container.
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