Stack和Queue（3）

Stack和Queue（3）

priority_queue的模拟实现

priority_queue.h

#include <vector>namespace soobin
{template<class T, class Container = vector<T>>class priority_queue{public://强制生成默认构造priority_queue() = default;template <class InputIterator>priority_queue(InputIterator first, InputIterator last):_con(first, last){//建堆//起始位置是最后一个非叶子节点的位置for (int i = (_con.size() - 1 - 1) / 2; i > 0; i--){AdjustDown(i);}}void AdjustUp(int child){int parent = (child - 1) / 2;while (child > 0){if (_con[child] > _con[parent]){swap(_con[child], _con[parent]);child = parent;parent = (parent - 1) / 2;}else{break;}}}void push(const T& x){_con.push_back(x);AdjustUp(_con.size() - 1);}void AdjustDown(int parent){size_t child = parent * 2 + 1;while (child < _con.size()){// 假设法，选出左右孩子中小的那个孩子if (child + 1 < _con.size() && _con[child + 1] > _con[child]){++child;}if (_con[child] > _con[parent]){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();AdjustDown(0);}bool empty(){return _con.empty();}const T& top(){return _con[0];}size_t size(){return _con.size();}private:Container _con;};
}

Test.cpp

#include<iostream>
#include<stack>
#include<queue>using namespace std;#include "priority_queue.h"int main()
{int a[] = { 1,4,2,5,6,3,2 };soobin::priority_queue<int> pq1(a, a + sizeof(a) / sizeof(int));//默认是大的优先级高soobin::priority_queue<int> pq;//小的优先级高的写法//priority_queue<int, vector<int>, less<int>> pq;pq.push(1);pq.push(2);pq.push(3);pq.push(4);while (!pq.empty()){cout << pq.top() << " ";pq.pop();}cout << endl;return 0;
}

仿函数

例子如下：

template <class T>struct less {bool operator() (const T& x, const T& y) const{ return x < y;}};template <class T>struct greater{bool operator() (const T& x, const T& y) const{return x > y;}};

是结构体，但是通过operator()进行重载

两个地方的应用：

1.比较大小怕与库里面的函数冲突

拿上面建堆来举例子：

#include <vector>namespace soobin
{template <class T>struct less{bool operator() (const T& x, const T& y) const{return x < y;}};template <class T>struct greater{bool operator() (const T& x, const T& y) const{return x > y;}};template<class T, class Container = vector<T>, class Compare = less<T>>//template<class T, class Container = vector<T>>class priority_queue{public://强制生成默认构造priority_queue() = default;template <class InputIterator>priority_queue(InputIterator first, InputIterator last):_con(first, last){//建堆//起始位置是最后一个非叶子节点的位置for (int i = (_con.size() - 1 - 1) / 2; i > 0; i--){AdjustDown(i);}}void AdjustUp(int child){Compare com;int parent = (child - 1) / 2;while (child > 0){//if (_con[child] > _con[parent])if(com(_con[child],_con[parent])){swap(_con[child], _con[parent]);child = parent;parent = (parent - 1) / 2;}else{break;}}}void push(const T& x){_con.push_back(x);AdjustUp(_con.size() - 1);}void AdjustDown(int parent){Compare com;size_t child = parent * 2 + 1;while (child < _con.size()){// 假设法，选出左右孩子中小的那个孩子//if (child + 1 < _con.size() && _con[child + 1] > _con[child])if (child + 1 < _con.size() && com(_con[child], _con[child + 1])){++child;}//if (_con[child] > _con[parent])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();AdjustDown(0);}bool empty(){return _con.empty();}const T& top(){return _con[0];}size_t size(){return _con.size();}private:Container _con;};
}

2.想要实现比较大小，但是不是我们预期效果的时候

class Date
{
public: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);}friend ostream& operator<<(ostream& _cout, const Date& d);
private:int _year;int _month;int _day;
};ostream& operator<<(ostream& _cout, const Date& d)
{_cout << d._year << "-" << d._month << "-" << d._day;return _cout;
}

int main()
{soobin::priority_queue<Date*> q1;q1.push(new Date{ 2024, 10, 23});q1.push(new Date{ 2024, 5, 27 });q1.push(new Date{ 2024, 11, 2 });while (!q1.empty()){cout << *q1.top() << " ";q1.pop();}cout << endl;return 0;
}

我们在实现上面日期类的时候，如果不去自己设置仿函数，编译器可能会比较指针，而不是里面的内容，需要自己去设置仿函数比较里面内容的大小