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priority_queue:

头文件就是queue

第一个是模版，第二个是容器适配器，第三个是仿函数

仿函数传less，出来是大堆

仿函数传greater，出来是小堆

底层是大堆，优先级高的“大”，在堆顶，取出来的有序，存的无序，pop堆顶

传类型： 

	//priority_queue<int> pq;// 小堆//A::priority_queue<int, deque<int>> pq;//A::priority_queue<int, vector<int>> pq;// 大堆//A::priority_queue<int> pq;// 小堆A::priority_queue<int, vector<int>, A::greater<int>> pq;pq.push(2);pq.push(1);pq.push(4);pq.push(3);pq.push(7);pq.push(8);while (!pq.empty()){cout << pq.top() << " ";pq.pop();}cout << endl;

传对象： 自动推演参数类型

	// 仿函数vector<int> v = { 3,1,7,4,6,3 };// 默认升序sort(v.begin(), v.end());for (auto e : v){cout << e << " ";}cout << endl;// 降序 >//greater<int> gt;//有名对象//sort(v.begin(), v.end(), gt);sort(v.begin(), v.end(), greater<int>());//使用匿名对象for (auto e : v){cout << e << " ";}cout << endl;

仿函数：

一个类只要重载了operator( )就叫仿函数，也就是说这个类的对象可以像函数一样使用，省略函数名，直接由对象调用

// 所有数据都公有，一般就用struct
// 有些公有，有些私有，一般就用class
// 
// 仿函数/函数对象
// 仿函数的对象可以像函数一样的去使用
template<class T>
class Less
{
public:bool operator()(const T& x, const T& y){return x < y;}
};int main(){Less<int> lessfunc;cout << lessfunc(1, 2) << endl;//有名对象cout << lessfunc.operator()(1, 2) << endl;cout << Less<int>()(1, 2) << endl;//匿名对象cout << Less<int>().operator()(1, 2) << endl;vector<int> v;v[0];v.operator[](0);
}

优先级队列内部实现：

容器适配器也可以用deque

C用函数指针控制，比较大小的函数

//仿函数template<class T>class less{public:bool operator()(const T& x, const T& y){return x < y;}};template<class T>class greater{public:bool operator()(const T& x, const T& y){return x > y;}};    //堆是完全二叉树，用的是数组实现的，所以这里优先级队列也用vector
//大堆template<class T, class Container = vector<T>, class Compare = less<T>>class priority_queue{public:void adjust_up(size_t child){Compare com;int parent = (child - 1) / 2;while (child > 0){//if (_con[child] > _con[parent])//if (_con[parent] < _con[child])if (com(_con[parent], _con[child]))//less{swap(_con[child], _con[parent]);child = parent;parent = (child - 1) / 2;}else{break;}}}void push(const T& x){_con.push_back(x);adjust_up(_con.size() - 1);}void adjust_down(size_t parent){Compare com;size_t child = parent * 2 + 1;while (child < _con.size()){//if (child + 1 < _con.size() && _con[child + 1] > _con[child])//if (child + 1 < _con.size() && _con[child] < _con[child + 1])if (child + 1 < _con.size() && com(_con[child], _con[child + 1]))//less{++child;}//if (_con[child] > _con[parent])//if (_con[parent] < _con[child])if (com(_con[parent], _con[child])){swap(_con[child], _con[parent]);parent = child;child = parent * 2 + 1;}else{break;}}}void pop(){swap(_con[0], _con[_con.size() - 1]);_con.pop_back();adjust_down(0);}bool empty(){return _con.empty();}size_t size(){return _con.size();}const T& top(){return _con[0];}private:Container _con;};//使用// 小堆A::priority_queue<int, vector<int>, A::greater<int>> pq;pq.push(2);pq.push(1);pq.push(4);pq.push(3);pq.push(7);pq.push(8);while (!pq.empty()){cout << pq.top() << " ";pq.pop();}cout << endl;

日期类：

class Date
{
public:friend ostream& operator<<(ostream& _cout, const Date& d);Date(int year = 1900, int month = 1, int day = 1): _year(year), _month(month), _day(day){}bool operator<(const Date& d)const{return (_year < d._year) ||(_year == d._year && _month < d._month) ||(_year == d._year && _month == d._month && _day < d._day);}bool operator>(const Date& d)const{return (_year > d._year) ||(_year == d._year && _month > d._month) ||(_year == d._year && _month == d._month && _day > d._day);}
private:int _year;int _month;int _day;
};ostream& operator<<(ostream& _cout, const Date& d)
{_cout << d._year << "-" << d._month << "-" << d._day;return _cout;
}//运算符重载必须至少有一个自定义类型
//这里两个都是内置类型，指针，所以不能这样重载
//bool operator<(const Date* d1, const Date* d2)
//{
//	return true;
//}class GreaterPDate
{
public:bool operator()(const Date* p1, const Date* p2){return *p1 > *p2;}
};void test_priority_queue2()
{A::priority_queue<Date, vector<Date>, A::greater<Date>> pq;Date d1(2024, 4, 8);pq.push(d1);//有名对象pq.push(Date(2024, 4, 10));//匿名对象pq.push({ 2024, 2, 15 });//隐式类型转换（临时对象）while (!pq.empty()){cout << pq.top() << " ";pq.pop();}cout << endl;//如果优先级队列里存的是指针
//可以重新写一个GreaterPDate，否则push之后比较的就是括号里东西的大小，也就是Date*，new的地址
//但是如果运算符重载必须至少有一个自定义类型，不能重载Date*也就是指针的比较大小A::priority_queue<Date*, vector<Date*>, GreaterPDate> pqptr;pqptr.push(new Date(2024, 4, 14));pqptr.push(new Date(2024, 4, 11));pqptr.push(new Date(2024, 4, 15));while (!pqptr.empty()){cout << *(pqptr.top()) << " ";pqptr.pop();}cout << endl;
}

商品类：

struct Goods
{string _name; // 名字double _price; // 价格int _evaluate; // 评价Goods(const char* str, double price, int evaluate):_name(str), _price(price), _evaluate(evaluate){}
};struct ComparePriceLess
{bool operator()(const Goods& gl, const Goods& gr){return gl._price < gr._price;}
};
struct ComparePriceGreater
{bool operator()(const Goods& gl, const Goods& gr){return gl._price > gr._price;}
};struct CompareEvaluateLess
{bool operator()(const Goods& gl, const Goods& gr){return gl._evaluate < gr._evaluate;}
};
struct CompareEvaluateGreater
{bool operator()(const Goods& gl, const Goods& gr){return gl._evaluate > gr._evaluate;}
};int main()
{vector<Goods> v = { { "苹果", 2.1, 5 }, { "香蕉", 3, 4 }, { "橙子", 2.2,3 }, { "菠萝", 1.5, 4 } };sort(v.begin(), v.end(), ComparePriceLess());sort(v.begin(), v.end(), ComparePriceGreater());sort(v.begin(), v.end(), CompareEvaluateLess());sort(v.begin(), v.end(), CompareEvaluateGreater());
}