easy way to maintain a min heap with stl?

Question

for user defined struct, as I understand, it\'s easy. Just overload the operator <. However, for int/float etc.., do I really need to overload operator < for int? Here is

Answer 1

The answers are good, so I just wanted to add a small example. Say you have the following array:

array<int, 10> A{5,2,8,3,4,1,9,12,0,7};

and you want to create a min heap. The quickest way to do that is to use make_heap algorithm. However, that creates a max heap by default. In other words, if you call:

make_heap(A.begin(), A.end());

A becomes a max heap. To have a min heap, on the other hand, you need to add a comparator but do not need to implement one. Instead call the method as follows:

make_heap(A.begin(), A.end(), greater<int>());

This call will make your array a min heap.

PS: #include <algorithm> is necessary to use std::make_heap. Same operations apply to the vector as well.

HTH!

Answer 2

You shouldn't need to overload operator < for int (you can't, actually). If you use an external comparator, you should be passing the same Comparator comp to pop_head as well.

* Edit: *

As ildjarn pointed out, your comparison operator does not implement a strict-weak-ordering relation.

a < b ? false : true; --> a >= b
b < a ? true : false; --> a > b

Answer 3

Use std::greater<int>() as the comparator(to all of make_heap, push_heap, pop_heap). The () are important - std::greater<int> is a functor class not a function, so you need an instance of it.