std :: make_heap与对

Question

Is it possible to do make_heap() with a pair in a vector?

I'm using:

 std::vector< std::pair < int , tablero& > > lista_abierta_;

I use the object function to order the pair by the first member, but it crashes.

The code is:

#include <iostream>
#include <vector>
#include <map>
#include <cmath>
#include <algorithm>
#include <functional>
#include "8_puzzle.h"
#include "tablero.h"

using namespace std;

class comp {
public:
    bool operator()(pair < int, tablero&> a, pair < int, tablero&> b) const {
        return a.first > b.first;
    }
};

pair < int, tablero& > puzzle::A_estrella::tope()
{
    pair < int, tablero& > l=lista_abierta_.front();

    pop_heap(lista_abierta_.begin(),lista_abierta_.end());
    lista_abierta_.pop_back();

    return l;
}

[Taken from here ]

Answer 1

只要std::pair<T, U>提供operator< （意思是： T和U提供operator< ），我就不会在使用make_heap时遇到任何问题。

Answer 2

You can call std::make_heap<T> as long as T provides bool operator<(const T &, const T &) or you explicitly pass comparer.

You have to change line 23 from

pop_heap(lista_abierta_.begin(),lista_abierta_.end());

to

pop_heap(lista_abierta_.begin(),lista_abierta_.end(), comp());

Answer 3

The issue is reference like pair < int, tablero& > won't work in case of copy inside make_heap / pop_heap . To fix that we need pair<int, std::reference_wrapper<tablero> > . The comp and other implementations need to be changed accordingly.

class comp {
public:
    bool operator()(pair < int, std::reference_wrapper<tablero> > a, pair < int, std::reference_wrapper<tablero> > b) const {
        return a.first > b.first;
    }
};

And heap_pop and make_heap will require an object of Compare .

comp mycomp;
pop_heap(lista_abierta_.begin(),lista_abierta_.end(),mycomp);