The default stl priority queue is a Max one (Top function returns the largest element).
Say, for simplicity, that it is a priority queue of int values.
+6
A:
Use std::greater as the comparison function:
std::priority_queue<int, std::vector<int>, std::greater<int> > my_min_heap;
James McNellis
2010-03-13 17:37:36
+1 You got it first ;)
AraK
2010-03-13 17:39:33
and if it is not priority queue of ints, but some MyClass object?
amitlicht
2010-03-13 17:43:23
@eriks You have some options. Either your class defines `operator>`, which would work like charm with `std::greater`. You could write your own functor also instead of `std::greater` if you like.
AraK
2010-03-13 17:45:07
@AraK, I think you mean `operator<` ;)
Peter Alexander
2010-03-13 17:46:05
@Poita_ Doesn't `std::greater` use `operator>` and `std::less` use `operator<`? Sorry if I am missing something.
AraK
2010-03-13 17:48:11
@AraK, @Poita_: Yes, `std::greater` uses `operator>`. @eriks: What AraK said above is the correct way to do this for user-defined types.
James McNellis
2010-03-13 17:53:05
The default comparison functor is less<T>, so logically, to reverse the order, you would use greater<T>.
David Smith
2010-03-21 14:40:11
+3
A:
The third template parameter for priority_queue is the comparator. Set it to use greater.
e.g.
std::priority_queue<int, std::vector<int>, std::greater<int> > max_queue;
You'll need #include <functional> for std::greater.
Peter Alexander
2010-03-13 17:45:32
`<queue>` is likely to include `<algorithm>` is very likely to include `<functional>`.
Potatoswatter
2010-03-14 04:22:43