关于C++中vector和set使用sort方法进行排序

C++中vector和set都是非常方便的容器,

sort方法是algorithm头文件里的一个标准函数,能进行高效的排序,默认是按元素从小到大排序

将sort方法用到vector和set中能实现多种符合自己需求的排序

首先sort方法可以对静态的数组进行排序

1 #include<iostream>
2 using namespace std;
3 int main(){
4     int a[10] = { 9, 0, 1, 2, 3, 7, 4, 5, 100, 10 };
5     sort(a, a +10);
6     for (int i = 0; i < 10; i++)
7         cout << a[i] << endl;
8     return 0;
9 }

运行结果:

 

这里可以看到是sort(a,a+10),但是数组a一共只有9个元素,为什么是a+10而不是a+9呢?

因为sort方法实际上最后一位地址对应的数是不取的,

而且vector,set,map这些容器的end()取出来的值实际上并不是最后一个值,而end的前一个才是最后一个值!

需要用prev(xxx.end()),才能取出容器中最后一个元素。

 

对vector使用sort函数:

第一种情形:基本类型,如vector<int>,vector<double>,vector<string>也是可以的

 1 #include<iostream>
 2 #include<vector>
 3 #include<algorithm>
 4 using namespace std;
 5 int main(){
 6     vector<int> a;
 7     int n = 5;
 8     while (n--){
 9         int score;
10         cin >> score;
11         a.push_back(score);
12     }
13     //cout <<" a.end()"<< *a.end() << endl;       执行这句话会报错!
14     cout << " prev(a.end)" << *prev(a.end()) << endl;
15     sort(a.begin(), a.end());
16     for (vector<int>::iterator it = a.begin(); it != a.end(); it++){
17         cout << *it << endl;
18     }
19     return 0;
20 }

执行结果:

看到了吗,实际上end的前一个指针指向的元素才是插入时的最后一个值!

排序后从小大大。

第二种情形:用自定义的结构体进行sort算法,

这时候需要自己定义个比较函数,因为sort算法是基于容器中的元素是可以两两比较的,然后从小到大排序,所以要自定义怎么样才是小于('<')

 1 #include<iostream>
 2 #include<vector>
 3 #include<set>
 4 #include<string>
 5 #include<algorithm>
 6 using namespace std;
 7 struct student{
 8     char name[10];
 9     int score;
10 };
11 //自定义“小于”
12 bool comp(const student &a, const student &b){
13     return a.score < b.score;
14 }
15 int main(){
16     vector<student> vectorStudents;
17     int n = 5;
18     while (n--){
19         student oneStudent;
20         string name;
21         int score;
22         cin >> name >> score;
23         strcpy(oneStudent.name, name.c_str());
24         oneStudent.score = score;
25         vectorStudents.push_back(oneStudent);
26     }
27     cout << "===========排序前================" << endl;
28     for (vector<student>::iterator it = vectorStudents.begin(); it != vectorStudents.end(); it++){
29         cout << "name: " << it->name << " score: " << it->score << endl;
30     }
31     sort(vectorStudents.begin(),vectorStudents.end(),comp);
32     cout << "===========排序后================" << endl;
33     for (vector<student>::iterator it = vectorStudents.begin(); it != vectorStudents.end(); it++){
34         cout << "name: " << it->name << " score: " << it->score << endl;
35     }
36     return 0;
37 }

运行结果:

 

不过有时候一个排序条件不够,比如要求学生按分数从高到低排序,如果分数相同,则按照年龄从大到小排序

就需要在comp自定义函数里面修改一下判断了,原来是直接return a.score < b.score

现在就需要判断

if (a.score > b.score)
   return true;
else if (a.score == b.score  && a.age > b.age)
return true; else return false;

这里一定要记得else return false!!!有一次比赛的时候写到这个函数,有三个判断条件,结果忘了这茬,总是报错,
到后来有点着急了就自己手动实现了一下写了三个比较函数,调用了三次sort函数!!!!!
 1 #include<iostream>
 2 #include<vector>
 3 #include<set>
 4 #include<string>
 5 #include<algorithm>
 6 using namespace std;
 7 struct student{
 8     char name[10];
 9     int score;
10     int age;
11 };
12 //自定义“小于”
13 bool comp(const student &a, const student &b){
14     if (a.score > b.score)
15         return true;
16     else if (a.score == b.score  && a.age > b.age)
17         return true;
18     else                ///这里的else return false非常重要!!!!!
19         return false;
20 }
21 int main(){
22     vector<student> vectorStudents;
23     /*set<student> setStudents;*/
24     //int n = 5;
25     int n = 6;
26     while (n--){
27         student oneStudent;
28         string name;
29         int score;
30         int age;
31         cin >> name >> score>>age;
32         strcpy(oneStudent.name, name.c_str());
33         oneStudent.score = score;
34         oneStudent.age = age;
35         vectorStudents.push_back(oneStudent);
36     }
37     cout << "===========排序前================" << endl;
38     for (vector<student>::iterator it = vectorStudents.begin(); it != vectorStudents.end(); it++){
39         cout << "name: " << it->name << " score: " << it->score << " age: "<<it->age<<endl;
40     }
41     sort(vectorStudents.begin(), vectorStudents.end(), comp);
42     //sort(setStudents.begin(), setStudents.end());
43     cout << "===========排序后================" << endl;
44     for (vector<student>::iterator it = vectorStudents.begin(); it != vectorStudents.end(); it++){
45         cout << "name: " << it->name << " score: " << it->score << " age: " << it->age << endl;
46     }
47     return 0;
48 }

运行结果如下:

接下来,对于set做类似的操作。

set是一个集合,内部的元素不会重复,同时它会自动进行排序,也是从小到大

而且set的insert方法没有insert(a,cmp)这种重载,所以如果要把结构体插入set中,我们就要重载'<'运算符。

set方法在插入的时候也是从小到大的,那么我们重载一下<运算符让它从大到小排序

 1 #include<iostream>
 2 #include<vector>
 3 #include<set>
 4 #include<string>
 5 #include<algorithm>
 6 using namespace std;
 7 struct student{
 8     char name[10];
 9     int score;
10 };
11 //自定义“小于”
12 bool comp(const student &a, const student &b){
13     return a.score < b.score;
14 }
15 bool operator < (const student & stu1,const student &stu2){
16     return stu1.score > stu2.score;
17 }
18 int main(){
19     //vector<student> vectorStudents;
20     set<student> setStudents;
21     //int n = 5;
22     int n = 6;
23     while (n--){
24         student oneStudent;
25         string name;
26         int score;
27         cin >> name >> score;
28         strcpy(oneStudent.name, name.c_str());
29         oneStudent.score = score;
30         setStudents.insert(oneStudent);
31     }
32     cout << "===========排序前================" << endl;
33     for (set<student>::iterator it = setStudents.begin(); it != setStudents.end(); it++){
34         cout << "name: " << it->name << " score: " << it->score << endl;
35     }
36     //sort(setStudents.begin(), setStudents.end(), comp);
37     //cout << "===========排序后================" << endl;
38     //for (set<student>::iterator it = setStudents.begin(); it != setStudents.end(); it++){
39     //    cout << "name: " << it->name << " score: " << it->score << endl;
40     //}
41     return 0;
42 }

运行结果:

我们可以看到,set内元素不会重复,而且它按照它所认为的“从小到大”进行了排序

 

posted @ 2016-06-04 00:31  不著人间风雨门  阅读(154781)  评论(0编辑  收藏  举报