I am trying to make a min-heap1 of long
s in C++ using the STL make_heap
, etc., but my comparator doesn't seem to be comparing properly. The following is my current comparator:
struct greater1{
bool operator()(const long& a,const long& b) const{
return a>b;
}
};
However, when I do std::pop_heap(humble.begin(),humble.end(),g);
where g
is an instance of greater1
and humble
is a heap who makes [9,15,15,25]
when sort_heap
is called, I get a 15
popped.
Is my comparator correct? what might be going wrong?
EDIT:
I realized that I am running sort_heap with no comparator, whereas when I run it this comparator, I get [15,15,9,25]
from sort_heap
. Now I am thinking my comparator is definitely not working, but unsure why.
1The STL makes a max-heap by default, so I need a comparator.
Perhaps you are missing something somewhere, the code below works as intended:
#include <vector>
#include <algorithm>
#include <iostream>
struct greater1{
bool operator()(const long& a,const long& b) const{
return a>b;
}
};
int main() {
std::vector<long> humble;
humble.push_back(15);
humble.push_back(15);
humble.push_back(9);
humble.push_back(25);
std::make_heap(humble.begin(), humble.end(), greater1());
while (humble.size()) {
std::pop_heap(humble.begin(),humble.end(),greater1());
long min = humble.back();
humble.pop_back();
std::cout << min << std::endl;
}
return 0;
}