deevee deevee - 1 month ago 8
C++ Question

How to specifiy comparison for pair?

There is a

pair


pair <string, int> myPair;


I have a
vector
of
myPair
objects. I need to convert it to a min-heap using
make_heap
on the second value of
pair
i.e. the integer. How can I do that? I am not sure on how to define the comparison operations.

I know I need something like this for heap to operate. But not sure where to put it:

bool operator< (const Pair& p1, const Pair& p2) const
{
return p1.second < p2.second;
}

Xeo Xeo
Answer

Well, make_heap has an overload that takes an extra comparision operator, soo...

// somewhere in global namespace
typedef std::pair<std::string, int> myPair_type;

struct mypair_comp{
  bool operator()(myPair_type const& lhs, myPair_type const& rhs){
    return lhs.second < rhs.second;
  }
};

// somewhere at your callside
make_heap(first,last,mypair_comp());
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