Is there a difference between using .begin() vs .end() for std::inserter for std::set?
If there is any difference between it1 and it2?
std::set<sometype> s;
auto it1 = std::i开发者_如何学Pythonnserter(s, s.begin());
auto it2 = std::inserter(s, s.end());
In practice, not much. If you're inserting a large number of already in order elements into an empty set
, the second will be somewhat faster, but that's about it. std::insert_iterator
calls insert
with the iterator; std::set
interprets it as a hint, and inserts in constant time (rather than lg n) if the insertion is immediately before the hint. (Actually, if the set
is empty, I think both will do exactly the same thing.)
From http://www.sgi.com/tech/stl/insert_iterator.html
In the case of a Sorted Associative Container, however, the iterator in the insert_iterator's constructor is almost irrelevant. The new elements will not necessarily form a contiguous range; they will appear in the appropriate location in the container, in ascending order by key. The order in which they are inserted only affects efficiency: inserting an already-sorted range into a Sorted Associative Container is an O(N) operation.
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