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


例子

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <map>
#include <unordered_map>
 

#include <string>
#include <queue>
using namespace std;


/**
預設比較函式為less, 大頂堆
**/
void defaultCmpLess() {
    cout << "=========defaultCmpLess(big heap)========" << endl;
    priority_queue<int> q;
    for (int i = 0; i < 10; i++) {
        q.push(rand()%20);
    }

    while
 
 (!q.empty()) {
        cout << q.top() << " ";
        q.pop();
    }
    cout <<endl;

}

/**
使用greater比較函式，小頂堆
**/
void useCmpGreater() {
    cout << "=========useCmpGreater(small heap)========" << endl;
    priority_queue<int, vector<int>, greater<int> > q;
    for
 
 (int i = 0; i < 10; i++) {
        q.push(rand()%20);
    }

    while (!q.empty()) {
        cout << q.top() << " ";
        q.pop();
    }
    cout <<endl;
}


//==========================

struct Node
{
    int x, y;
    Node(int a = 0, int b = 0):x(a), y(b){};
    friend bool operator<(const Node &a, const Node &b);

};
inline bool operator<(const Node &a, const Node &b) {
    if (a.x != b.x)
        return a.x < b.x;
    return a.y > b.y;
}

/**
運算子過載
**/
void overloadOperator() {
    cout << "=========overload Operator< =========" << endl;
    cout << "a.x < b.x; a.y > b.y" << endl;
    priority_queue<Node> q;
    for (int i = 0; i < 10; i++) {

        q.push( Node( rand()%20, rand()%20 ) );
    }

    while (!q.empty()) {
        cout << q.top().x << "," << q.top().y << endl;
        q.pop();
    } 
    cout << endl;   
}


//=========================
/**
自構建比較函式
**/
struct cmp2
{
    bool operator()(int a, int b) {
        return a < b;
    }
};

void designCmp() {
    cout << "=========designCmp========" << endl;
    cout << "operator a<b" << endl;
    priority_queue<int, vector<int>, cmp2 > q;

    for (int i = 0; i < 10; i++) {
        q.push(rand()%20);
    }

    while (!q.empty()) {
        cout << q.top() << " ";
        q.pop();
    }
    cout <<endl;
}

int main(int argc, char const *argv[])
{   
    defaultCmpLess();
    useCmpGreater();
    overloadOperator();
    designCmp();
}


/**
=========defaultCmpLess(big heap)========
18 18 13 12 10 9 9 7 4 3
=========useCmpGreater(small heap)========
0 0 2 3 5 7 7 9 12 12
=========overload Operator< =========
a.x < b.x; a.y > b.y
19,1
19,9
19,18
17,6
16,15
12,7
10,13
9,17
3,9
0,13

=========designCmp========
operator a<b
17 16 14 13 12 11 8 7 5 5

**/