关于排序等规则

关于优先队列：

请注意reference中的这段描述

Priority queue

Priority queues are a type of container adaptors, specifically designed such that its first element is always the greatest of the elements it contains, according to some strict weak ordering criterion.

This context is similar to a heap, where elements can be inserted at any moment, and only the max heap element can be retrieved (the one at the top in the priority queue).

Priority queues are implemented as container adaptors, which are classes that use an encapsulated object of a specific container class as its underlying container, providing a specific set of member functions to access its elements.Elements are popped from the "back" of the specific container, which is known as the top of the priority queue.

我只想让小的元素处于队列顶端，那么就可以只改变<的判断方式，其他不改变，那么就只重载了小于。

/*优先队列的基本使用    2010/7/24    dooder*/  
#include<stdio.h>  
#include<functional>  
#include<queue>  
#include<vector>  
using namespace std;  
//定义结构，使用运算符重载,自定义优先级1  
struct cmp1{  
    bool operator ()(int &a,int &b){  
        return a>b;//最小值优先  
    }  
};  
struct cmp2{  
    bool operator ()(int &a,int &b){  
        return a<b;//最大值优先  
    }  
};  
//定义结构，使用运算符重载,自定义优先级2  
struct number1{  
    int x;  
    bool operator < (const number1 &a) const {  
        return x>a.x;//最小值优先  
    }  
};  
struct number2{  
    int x;  
    bool operator < (const number2 &a) const {  
        return x<a.x;//最大值优先  
    }  
};  
int a[]={14,10,56,7,83,22,36,91,3,47,72,0};  
number1 num1[]={14,10,56,7,83,22,36,91,3,47,72,0};  
number2 num2[]={14,10,56,7,83,22,36,91,3,47,72,0};  
  
int main()  
{   priority_queue<int>que;//采用默认优先级构造队列  
  
    priority_queue<int,vector<int>,cmp1>que1;//最小值优先  
    priority_queue<int,vector<int>,cmp2>que2;//最大值优先  
  
    priority_queue<int,vector<int>,greater<int> >que3;//注意“>>”会被认为错误，  
                                                      //这是右移运算符，所以这里用空格号隔开  
    priority_queue<int,vector<int>,less<int> >que4;////最大值优先  
  
    priority_queue<number1>que5;  
    priority_queue<number2>que6;  
  
    int i;  
    for(i=0;a[i];i++){  
        que.push(a[i]);  
        que1.push(a[i]);  
        que2.push(a[i]);  
        que3.push(a[i]);  
        que4.push(a[i]);  
    }  
    for(i=0;num1[i].x;i++)  
        que5.push(num1[i]);  
    for(i=0;num2[i].x;i++)  
        que6.push(num2[i]);  
  
  
    printf("采用默认优先关系:\n(priority_queue<int>que;)\n");  
    printf("Queue 0:\n");  
    while(!que.empty()){  
        printf("%3d",que.top());  
        que.pop();  
    }  
    puts("");  
    puts("");  
  
    printf("采用结构体自定义优先级方式一:\n(priority_queue<int,vector<int>,cmp>que;)\n");  
    printf("Queue 1:\n");  
    while(!que1.empty()){  
        printf("%3d",que1.top());  
        que1.pop();  
    }  
    puts("");  
    printf("Queue 2:\n");  
    while(!que2.empty()){  
        printf("%3d",que2.top());  
        que2.pop();  
    }  
    puts("");  
    puts("");  
    printf("采用头文件\"functional\"内定义优先级:\n(priority_queue<int,vector<int>,greater<int>/less<int> >que;)\n");  
    printf("Queue 3:\n");  
    while(!que3.empty()){  
        printf("%3d",que3.top());  
        que3.pop();  
    }  
    puts("");  
    printf("Queue 4:\n");  
    while(!que4.empty()){  
        printf("%3d",que4.top());  
        que4.pop();  
    }  
    puts("");  
    puts("");  
    printf("采用结构体自定义优先级方式二:\n(priority_queue<number>que)\n");  
    printf("Queue 5:\n");  
    while(!que5.empty()){  
        printf("%3d",que5.top());  
        que5.pop();  
    }  
    puts("");  
    printf("Queue 6:\n");  
    while(!que6.empty()){  
        printf("%3d",que6.top());  
        que6.pop();  
    }  
    puts("");  
    return 0;  
}  
/* 
运行结果 ： 
采用默认优先关系: 
(priority_queue<int>que;) 
Queue 0: 
 91 83 72 56 47 36 22 14 10  7  3 
 
采用结构体自定义优先级方式一: 
(priority_queue<int,vector<int>,cmp>que;) 
Queue 1: 
  3  7 10 14 22 36 47 56 72 83 91 
Queue 2: 
 91 83 72 56 47 36 22 14 10  7  3 
 
采用头文件"functional"内定义优先级: 
(priority_queue<int,vector<int>,greater<int>/less<int> >que;) 
Queue 3: 
  3  7 10 14 22 36 47 56 72 83 91 
Queue 4: 
 91 83 72 56 47 36 22 14 10  7  3 
 
采用结构体自定义优先级方式二: 
(priority_queue<number>que) 
Queue 5: 
  3  7 10 14 22 36 47 56 72 83 91 
Queue 6: 
 91 83 72 56 47 36 22 14 10  7  3 
*/

关于 sort（）函数

关于greater<> 

里面bool operator() (const T& x, const T& y)的含义；

Member function returning whether the first argument compares greater than the second (x>y).

// greater example
#include <iostream>     // std::cout
#include <functional>   // std::greater
#include <algorithm>    // std::sort

int main () {
  int numbers[]={20,40,50,10,30};
  std::sort (numbers, numbers+5, std::greater<int>());
  for (int i=0; i<5; i++)
    std::cout << numbers[i] << ' ';
  std::cout << '\n';
  return 0;
}

自定义struct类型，用于sort排序

/*
 *关于自定义数据类型的sort使用方法
 *
 *@作者：张海波 zhang haibo
 *@时间：2013-12-1
 */

#include<algorithm>
#include<vector>
#include<iostream>
using namespace std;

//定义结构体
struct Type{
      int a;
      double b;
      //升序需要的操作符函数
      bool operator < (const Type& right) const 
      {
          return a < right.a;
      }//asscend
      //降序需要的操作符函数
      bool operator > (const Type& right) const
      {
          return a > right.a;
      }//desscend
};

//打印
void PrintVec(const vector<Type>& types);

//主函数
int main(int argc, char** argv)
{
	//初始化
	const int SIZE = 10;
	vector<Type> tests;
	for(int i = 0; i < SIZE; ++i)
	{
		Type ty;
		ty.a = i;
		tests.push_back(ty);
	}

	//升序
	sort(tests.begin(), tests.end(), less<Type>());
	PrintVec(tests);

	//降序
	sort(tests.begin(), tests.end(), greater<Type>());
	PrintVec(tests);
}

//打印
void PrintVec(const vector<Type>& types)
{
	if(types.empty())
		return;
	int size = types.size();
	for(int i = 0; i < size; ++i)
		cout << types[i].a << " ";
	cout << endl;	
}