STL排序算法sort

要使用STL中的算法，需要在程序头文件引入#include <algorithm>

1.对基本类型的数组从小到大排序: 

sort(数组名+n1，数组名+n2）;

n1和n2都是int类型的表达式，可以包含变量

如果n1=0,则 + n1可以不写 

将数组中下标范围为[n1,n2)的元素从小到大排序。下标为n2的元素不在排序区间内 

2.对元素类型为T的基本类型数组从大到小排序：

 sort(数组名+n1，数组名+n2,greater<T>()）;

3.用自定义的排序规则，对任何类型T的数组排序

 sort(数组名+n1，数组名+n2,排序规则结构名());

 排序规则结构的定义方式： 

 struct  排序规则结构名 {  bool operator()( const T & a1,const T & a2) {

              //若a1应该在a2前面，则返回true，否则返回false。 

                        }

}; 

例1：

  int a[] = {15,4,3,9,7,2,6};  sort(a,a+7); //对整个数组从小到大排序

  int a[] = {15,4,3,9,7,2,6};  sort(a,a+3); // 结果：{3,4,15,9,7,2,6}

  int a[] = {15,4,3,9,7,2,6};  sort(a+2,a+5); //结果：{15,4,3,7,9,2,6} 

例2：

int a[] = {15,4,3,9,7,2,6};

sort(a+1,a+4,greater<int>()); // 结果：{15,9,4,3,7,2,6} 

例3：

#include <iostream>

#include <cstring>

#include <algorithm>

using namespace std;

struct Student {

char name[20]; 

int id;

 double gpa;

};

Student students [] = { {"Jack",112,3.4},{"Mary",102,3.8},{"Mary",117,3.9}, {"Ala",333,3.5},{"Zero",101,4.0}}; 

struct StudentRule1 { //按姓名从小到大排  

bool operator() (const Student & s1,const Student & s2) {

 if( stricmp(s1.name,s2.name) < 0)

       return true; 

  return false;

         }

};

struct StudentRule2 { //按id从小到大排

    bool operator() (const Student & s1,const Student & s2) {

                return s1.id < s2.id;

         }

};

struct StudentRule3 {//按gpa从高到低排 

bool operator() (const Student & s1,const Student & s2) {   return s1.gpa > s2.gpa;

         }

};

void PrintStudents(Student s[],int size){ 

for(int i = 0;i < size;++i)   

cout << "(" << s[i].name << "," << s[i].id <<"," << s[i].gpa << ") " ;  cout << endl;

}

int main()

{

int n = sizeof(students) / sizeof(Student);  

 sort(students,students+n,StudentRule1()); //按姓名从小到大排     

PrintStudents(students,n);    

sort(students,students+n,StudentRule2()); //按id从小到大排   

 PrintStudents(students,n);    

sort(students,students+n,StudentRule3()); //按gpa从高到低排  

 PrintStudents(students,n);   

 return 0;

} 

结果：

(Ala,333,3.5) (Jack,112,3.4) (Mary,102,3.8) (Mary,117,3.9) (Zero,101,4)

(Zero,101,4) (Mary,102,3.8) (Jack,112,3.4) (Mary,117,3.9) (Ala,333,3.5)

(Zero,101,4) (Mary,117,3.9) (Mary,102,3.8) (Ala,333,3.5) (Jack,112,3.4)