C++优先队列按对象的特定方法升序排列

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问题描述

假设我有一个名为 MyClass 的类，每个 MyClass 对象都有一个名为 xVal 的方法.我想要的是按 MyClass.xVal()

Lets say I have the a class called MyClass and every MyClass object has a method called xVal. What I want is a priority queue of MyClass objects sorted in ascending order of MyClass.xVal()

到目前为止，我有这个:

So far I have this:

priority_queue<MyClass, vector<MyClass>, greater<MyClass>> queue;

当然，它没有达到我的预期.我遵守了但对我的对象使用了一些随机排序.如果有人能指出我做错了什么，我将不胜感激.

Of course, it doesn't do what I expect.I complies but uses some random ordering for my objects. Would appreciate it if someone can point out what I am doing wrong.

谢谢.

推荐答案

CPP 参考链接到优先队列规定优先队列可以定义为:

The CPP Reference link to Priority Queue provides that a priority queue can be defined as:

template<
    class T,
    class Container = std::vector<T>,
    class Compare = std::less<typename Container::value_type>
> class priority_queue;

这里，T=MyClass 和 Container=std::vector.唯一剩下的是 Compare ，正如上面提到的，可以使用 Lambdas 或 Functors 来实现.我会同时展示:

Here, T=MyClass and Container=std::vector<MyClass>. The only thing that remains is Compare which as has been mentioned above can be implemented using either Lambdas or Functors. I'll show both:

假设类定义如下，xVal() 方法的返回值作为排序键:

Let's say the class is defined as shown below with xVal() method's return value as the sort key:

struct MyClass{
    int count;
    int key;
    int xVal() { return count; };
};

使用 Lambda

//  Lambda skeleton: [capture preferences](arguments){ body }
auto cmp = [](MyClass left, MyClass right) {return left.xVal() > right.xVal();};
std::priority_queue<MyClass, std::vector<MyClass>, decltype(cmp)> queue(cmp);

使用函子

struct CmpFunctor{
    bool operator()(MyClass left, MyClass right) const {
        return left.xVal() > right.xVal();
    }
};
auto cmp = CmpFunctor()
std::priority_queue<MyClass, std::vector<MyClass>, decltype(cmp)> queue(cmp);

这是一个显示运行代码的链接.

Here is a link showing the running code.

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