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C++基础:C++标准库之set简介
1、综述
set是C++STL中众多的Container(容器)之一,用于储存数据并且能从一个数据集合中取出数据,它的每个元素的值必须惟一。set内部通过自建红黑树(一种非严格意义上的平衡二叉树)实现,可以对数据自动排序。构造set集合主要目的是为了快速检索,不可直接去修改键值。
2、set的常见操作
首先,在使用map之前需包含头文件#include<set>,下面简要介绍map的常见操作,详细信息可参见http://www.cplusplus.com/reference/set/set/
(1)构造函数:
构造函数有多种实现形式,如下举例:
set<int> Myset1; int Myint[] = {2,4,6,8,10}; set<int> Myset2(Myint,Myint+5); set<int> Myset3(Myset2); set<int> Myset4(Myset2.begin(),Myset2.end());
示例中int是set中数据类型,可以为其他类型,如char,float。
(2)插入数据:
for (int i=1; i<=5; ++i) //插入1 2 3 4 5 Myset1.insert(i); int Myint3[] = {3,6,9,12,15}; Myset3.insert(Myint3,Myint3+5);
(3)查找元素:
利用find()方法,find()函数返回一个对应查找值迭代器,如果没找到就返回指向set尾部的迭代器。
set<int>::iterator itr;//迭代器itr = Myset1.find(3);//查找2 if(itr!= Myset1.end()) cout<<"在Myset1找到元素3!"<<endl; else cout<<"在Myset1找不到元素3!"<<endl;
(4)元素遍历:
利用迭代器实现,也可以进行逆向遍历。示例如下:
cout<<"\nMyset1中元素内容如下:"<<endl; for(itr = Myset1.begin();itr!=Myset1.end();itr++) cout<<*itr<<" "; cout<<"\nMyset4中元素内容如下:"<<endl; itr = Myset4.begin(); while(itr != Myset4.end()) cout<<*itr ++ << " "; //逆向遍历Myset4 cout<<"\nMyset4逆向遍历结果如下:"<<endl; set<int>::reverse_iterator itr2 = Myset4.rbegin(); while(itr2 != Myset4.rend()) cout<<*itr2++ << " "; cout<<endl;
(5)元素删除:
采用erase()方法实现:
for(int i = 1;i<=5;i++) Myset3.erase(i*2); //或者用itr删除, itr = Myset4.begin(); itr ++;//此时itr指向第二个元素 Myset4.erase(itr); //删除多个元素 itr = Myset4.find(6); Myset4.erase(itr,Myset4.end());
(6)swap()方法:
实现的是对两个set的整体交换。
Myset1.swap(Myset2);
(7)size()方法:
返回set的大小,即元素的个数。
(8)empty()方法
判断map是否为空,若map为空,则返回true。
(9)begin()方法:
返回指向map头部的迭代器
(10)end()方法:
返回指向map尾部的迭代器
(11)clear()方法:
清除整个set的内容
3、常见操作程序示例
#include<iostream> #include<set> using namespace std; void test_set() { //四种构造函数形式举例 set<int> Myset1; int Myint2[] = {2,4,6,8,10}; set<int> Myset2(Myint2,Myint2 + 5); set<int> Myset3(Myset2); set<int> Myset4(Myset2.begin(),Myset2.end()); //插入数据 for (int i=1; i<=5; ++i) //插入1 2 3 4 5 Myset1.insert(i); int Myint3[] = {3,15,9,6,12};//尽管数组本身,但插入set之后是有序的,且注意对于重复元素(6)是不能重复插入的 Myset3.insert(Myint3,Myint3+5); //查找操作 set<int>::iterator itr;//迭代器 itr = Myset1.find(3);//查找2 if(itr!= Myset1.end()) cout<<"在Myset1找到元素3!"<<endl; else cout<<"在Myset1找不到元素3!"<<endl; //元素遍历,两种形式 cout<<"\nMyset1中元素内容如下:"<<endl; for(itr = Myset1.begin();itr!=Myset1.end();itr++) cout<<*itr<<" "; cout<<"\nMyset2中元素内容如下:"<<endl; for(itr = Myset2.begin();itr!=Myset2.end();itr++) cout<<*itr<<" "; cout<<"\nMyset3中元素内容如下:"<<endl; for(itr = Myset3.begin();itr!=Myset3.end();itr++) cout<<*itr<<" "; cout<<"\nMyset4中元素内容如下:"<<endl; itr = Myset4.begin(); while(itr != Myset4.end()) cout<<*itr ++ << " "; //逆向遍历Myset4 cout<<"\nMyset4逆向遍历结果如下:"<<endl; set<int>::reverse_iterator itr2 = Myset4.rbegin(); while(itr2 != Myset4.rend()) cout<<*itr2++ << " "; cout<<endl; //删除操作 for(int i = 1;i<=5;i++) Myset3.erase(i*2); cout<<"\nMyset3删除元素之后内容如下:"<<endl; for(itr = Myset3.begin();itr!=Myset3.end();itr++) cout<<*itr<<" "; //或者用itr删除, itr = Myset4.begin(); itr ++;//此时itr指向4 Myset4.erase(itr); cout<<"\nMyset4删除元素之后内容如下:"<<endl; for(itr = Myset4.begin();itr!=Myset4.end();itr++) cout<<*itr<<" "; itr = Myset4.find(6); Myset4.erase(itr,Myset4.end()); cout<<"\nMyset4再次删除元素之后内容如下:"<<endl; for(itr = Myset4.begin();itr!=Myset4.end();itr++) cout<<*itr<<" "; //交换 Myset1.swap(Myset2); cout<<"Myset1与Myset2进行交换"<<endl; cout<<"\n交换后Myset1内容如下:"<<endl; for(itr = Myset1.begin();itr!=Myset1.end();itr++) cout<<*itr<<" "; cout<<"\n交换后Myset2内容如下:"<<endl; for(itr = Myset2.begin();itr!=Myset2.end();itr++) cout<<*itr<<" "; cout<<endl; //清除与求大小 cout<<"\nMyset1大小为:"<<Myset1.size()<<endl; Myset1.clear(); cout<<"clear()清除Myset1的所有元素后大小为"<<Myset1.size()<<endl; }