Question

我需要使用“Heap”,这样一来就检索了STL,但似乎并没有奏效,我写了一些法典来解释:

#include <stdio.h>
#include <stdlib.h>
#include <vector>
#include <algorithm>

struct data
{
    int indice;
    int tamanho;
};


bool comparator2(const data* a, const data* b)
{
    return (a->tamanho < b->tamanho);
}

int main()
{

        std::vector<data*> mesas;

        data x1, x2, x3, x4, x5;

        x1.indice = 1;
        x1.tamanho = 3;

        x2.indice = 2;
        x2.tamanho = 5;

        x3.indice = 3;
        x3.tamanho = 2;

        x4.indice = 4;
        x4.tamanho = 6;

        x5.indice = 5;
        x5.tamanho = 4;

        mesas.push_back(&x1);

        mesas.push_back(&x2);

        mesas.push_back(&x3);

        mesas.push_back(&x4);

        mesas.push_back(&x5);


        make_heap(mesas.begin(), mesas.end(), comparator2);

        for(int i = 0 ; i < 5 ; i++)
        {
            data* mesa = mesas.front();
            pop_heap(mesas.begin(),mesas.end());
            mesas.pop_back();

            printf("%d, %d
", mesa->indice, mesa->tamanho);
        }

    return 0;
};

而这正是:

4, 6
2, 5
1, 3
3, 2
5, 4

因此,由于病媒上的最大元素没有被退回,因此它不会发挥巨大的作用。

或者说是错了吗?

Answer 1

需要通过<代码>comparator2至std:pop_heap<>code。既然如此,你是如何创造出的。否则,它将使用低于操作者的缺省,仅仅比较点值。

Answer 2


MSN的答案是正确的。 然而,两种风格的准则都能够防止这一错误:


宣布参照国而非标的参照国为operator<。 使用<条码>物体,而不是点码。

bool comparator2(const data& a, const data& b)
{
    return (a.tamanho < b.tamanho);
}


你可能真的需要点击器的载体,在这种情况下,这并不适用。

使用<代码>std: 优先权_queue(从<queue>到pop_heap和pop_back,供您参考。这需要一位分析员:

struct comparator2 { bool operator()(const data& a, const data& b)
{
    return (a.tamanho < b.tamanho);
} };
 
std::priority_queue<data, vector<data>, comparator2> mesas;
 // or std::priority_queue<data, vector<data>, comparator2>
mesas.push(x1);

最常见的方法是将这一缺省比较用于<条码>数据:

struct data
{
    int indice;
    int tamanho;
     
    friend bool operator<(const data& a, const data& b)
    {
        return (a.tamanho < b.tamanho);
    }
};
std::priority_queue<data> mesas;
mesas.push(x1);

也可使用一个未填充的集装箱,将予以复制。

Answer 3

st:

#include <stdio.h>
#include <stdlib.h>
#include <vector>
#include <algorithm>
#include <set>

struct data
{
    // Always put constructors on.
    // When the constructor is finished the object is ready to be used.
    data(int i,int t)
        :indice(i)
        ,tamanho(t)
    {}

    int indice;
    int tamanho;

    // Add the comparator to the class.
    // Then you know where to look for it.
    bool operator<(data const& b) const
    {
        return (tamanho < b.tamanho);
    }
};



int main()
{

        std::set<data> mesas;

        // Dont declare all your variables on the same line.
        // One per line otherwise it is hard to read.
        data x1(1,3);
        data x2(2,5);
        data x3(3,2);
        data x4(4,6);
        data x5(5,4);

        mesas.insert(x1);
        mesas.insert(x2);
        mesas.insert(x3);
        mesas.insert(x4);
        mesas.insert(x5);
        // You don t actually need the variables.
        // You could have done it in place.
        mesas.insert(data(6,100));

        // Use iterator to loop over containers.
        for(std::set<data>::iterator loop = mesas.begin(); loop != mesas.end(); ++loop)
        {
            printf("%d, %d
", loop->indice, loop->tamanho);
        }

    return 0;
};

Answer 4

我有同样的问题,能够以这样的方式解决:

struct comparator2 { bool operator()(data const * const a, data const * const b)
{
    return (a->tamanho < b->tamanho);
 } };

std::priority_queue<data*, std::vector<data*>, comparator2> mesas;

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