C++-priority_queue

C+±priority_queue

C++ STL-priority_queue 用法

priority_queue存在于头文件<queue>中，以下代码解释了该容器如何使用

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <queue>
#include <vector>

using namespace std;

struct Node{
    int a,b;
    Node(){}
    Node(int aa,int bb):a(aa),b(bb){}

    // 二级排序，a相同时按照b升序排序，否则按照a升序排序
    // (a,b): (1,1)<(1,2)<(2,1)<(2,2)
    // 这里重载的大于号和小于号在逻辑上等价
    bool operator < (const Node &r) const{
        if(a==r.a)
            return b<r.b;
        else
            return a<r.a;
    }
    bool operator > (const Node &r) const{
        if(a==r.a)
            return b>r.b;
        else
            return a>r.a;
    }
};

int main(){

    //priority_queue 是基于堆实现的优先队列

    // .size()返回当前优先队列的元素个数
    // empty()为true表示当前队列为空，false表示不空
    priority_queue<int> tmp_q;
    cout<<tmp_q.size()<<endl;   //0
    cout<<tmp_q.empty()<<endl;  //1
    tmp_q.push(1);
    cout<<tmp_q.size()<<endl;   //1
    cout<<tmp_q.empty()<<endl;  //0
    tmp_q.pop();
    cout<<tmp_q.size()<<endl;   //0
    cout<<tmp_q.empty()<<endl;  //1

    // priority_queue<int> 表示队列中存储的元素是int类型（STL模板类）
    // 默认priority_queue表示队列按照less出队
    // 后出队的元素比先出队的元素要小，出队的元素越来越小，所以是less
    // push 加入元素
    // top 返回队首元素
    // pop 队首元素出队
    priority_queue<int> q;  
    q.push(5);
    q.push(6);
    cout<<q.top()<<endl;        //6
    q.pop();
    cout<<q.top()<<endl;        //5
    q.pop();

    // greater 表示后出队的元素比先出队的元素要大, 出队的元素越来越大，所以是greater
    priority_queue<int, vector<int>, greater<int>> q_greater;
    // <>中第二个参数vector<int>表示优先队列中使用vector<int> 存储元素，可以更换成deque
    // 第二个参数中更换的其他类型应支持.begin(),.end(),.push(),.pop()等操作
    //  绝大多数情况都使用vector<>，极少需要更换
    // 例子：priority_queue<int, deque<int>, greater<int>> q_greater;
    q_greater.push(5);
    q_greater.push(6);
    cout<<q_greater.top()<<endl;    //5
    q_greater.pop();
    cout<<q_greater.top()<<endl;    //6
    q_greater.pop();

    // 更换为double类型，出队法则是less
    priority_queue<double, vector<double>, less<double>> q_less;
    q_less.push(5.2);
    q_less.push(6.6);
    cout<<q_less.top()<<endl;       //6.6
    q_less.pop();
    cout<<q_less.top()<<endl;       //5.2
    q_less.pop();

    // 自定义类Node的priority_queue 使用greater需要对元素重载大于号
    priority_queue<Node, vector<Node>, greater<Node>> q_greater_node;
    q_greater_node.push(Node(1,1));
    q_greater_node.push(Node(1,2));
    q_greater_node.push(Node(2,1));
    q_greater_node.push(Node(2,2));
    cout<<q_greater_node.top().a<<" "<<q_greater_node.top().b<<endl;    // 1 1
    q_greater_node.pop();
    cout<<q_greater_node.top().a<<" "<<q_greater_node.top().b<<endl;    // 1 2
    q_greater_node.pop();
    cout<<q_greater_node.top().a<<" "<<q_greater_node.top().b<<endl;    // 2 1
    q_greater_node.pop();
    cout<<q_greater_node.top().a<<" "<<q_greater_node.top().b<<endl;    // 2 2
    q_greater_node.pop();

    // 自定义类Node的priority_queue 使用less需要对元素重载小于号
    priority_queue<Node, vector<Node>, less<Node>> q_less_node;
    q_less_node.push(Node(1,1));
    q_less_node.push(Node(1,2));
    q_less_node.push(Node(2,1));
    q_less_node.push(Node(2,2));
    cout<<q_less_node.top().a<<" "<<q_less_node.top().b<<endl;  // 2 2 
    q_less_node.pop();
    cout<<q_less_node.top().a<<" "<<q_less_node.top().b<<endl;  // 2 1
    q_less_node.pop();
    cout<<q_less_node.top().a<<" "<<q_less_node.top().b<<endl;  // 1 2
    q_less_node.pop();
    cout<<q_less_node.top().a<<" "<<q_less_node.top().b<<endl;  // 1 1
    q_less_node.pop();

    return 0;
}