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1.概念

map中所有元素都是pair<key,value>，key 是map的键，value 是map的值

所有元素都会根据key自动排序

map/multimap属于关联式容器，底层结构是用二叉树实现。

map和multimap区别：

• map不允许容器中有重复key值元素

• multimap允许容器中有重复key值元素

2.map构造和赋值

map<T1,T2> mp;

map(const map &mp);// 拷贝构造

map &operator=(const map &mp);

#include <iostream>
#include <map>using namespace std;void printMap(const map<int,int> &mp)
{for(map<int,int>::const_iterator it = mp.begin(); it != mp.end(); it++){cout << "key = " << it->first << " value = " << it->second << endl;}cout<<endl;
}void test(){map<int,int> m;m.insert(pair<int,int>(1,10));m.insert(pair<int,int>(2,20));m.insert(pair<int,int>(3,30));printMap(m);map<int,int>m2(m);// 拷贝构造printMap(m2);map<int,int>m3;m3 = m2;// 赋值printMap(m3);}int main()
{test();system("pause");return 0;
}

3.map大小和交换

#include <iostream>
#include <map>using namespace std;void printMap(map<int, int> &m){for (map<int, int>::iterator it = m.begin(); it != m.end(); it++){cout << "key = " << it->first << " value = " << it->second << endl;}cout<<endl;
}
void test(){map<int,int> m;m.insert(pair<int,int>(1,10));m.insert(pair<int,int>(2,20));m.insert(pair<int,int>(3,30));if (m.empty()){cout<<"map为空"<<endl;}else{cout<<"map不为空"<<endl;cout<<"map的大小为："<<m.size()<<endl;}map<int,int>m2(m);map<int,int>m3;m3.insert(pair<int,int>(4,40));m3.insert(pair<int,int>(5,50));m3.insert(pair<int,int>(6,60));m3.swap(m2);printMap(m3);}int main()
{test();system("pause");return 0;
}

4.map插入和删除

insert(elem);

clear();

erase(pos);// 删除pos位置的元素,返回删除元素的下一个位置

erase(beg,end);// 删除beg到end之间的元素，左闭右开

erase(key);// 删除key对应的元素

#include <iostream>
#include <map>using namespace std;void printMap(const map<int,int> &m){for(map<int,int>::const_iterator it=m.begin();it!=m.end();it++){cout<<it->first<<" "<<it->second<<endl;}cout<<endl;
}void test(){map<int,int> m;m.insert(pair<int,int>(1,10));m.insert(make_pair(2,20));m.insert(map<int,int>::value_type(3,30));m[4]=40;printMap(m);//删除m.erase(m.begin());printMap(m);m.erase(3);printMap(m);//清空m.clear();m.erase(m.begin(),m.end());printMap(m);
}int main()
{test();system("pause");return 0;
}

5. map查找和统计

find(key);// 查找key对应的value,不存在返回end()

count(key);// 统计key出现的次数

#include <iostream>
#include <map>using namespace std;void printMap(map<int, int> &m)
{for (map<int, int>::iterator it = m.begin(); it != m.end(); it++){cout << "key = " << it->first << " value = " << it->second << endl;}cout<<endl;
}void test(){map<int, int>m; m.insert(pair<int, int>(1, 10));m.insert(pair<int, int>(2, 20));m.insert(pair<int, int>(3, 30));auto pos=m.find(3);// auto自动推导迭代器类型if(pos!=m.end()){cout<<"key = "<<pos->first<<" value = "<<pos->second<<endl;}else{cout<<"没有找到key = 3"<<endl;}int num=m.count(1);cout<<"key = 1 出现的次数 = "<<num<<endl;
}int main()
{test();system("pause");return 0;
}

 6. map容器排序

map容器默认排序规则为 按照key值进行 从小到大排序

#include <iostream>
#include <map>using namespace std;class MyCompare{public:bool operator()(int v1,int v2) const{return v1>v2;}
};void test(){map<int, int, MyCompare> m;m.insert(make_pair(1, 10));m.insert(make_pair(2, 20));m.insert(make_pair(3, 30));m.insert(make_pair(4, 40));m.insert(make_pair(5, 50));for (map<int, int,MyCompare>::const_iterator it = m.begin(); it != m.end(); it++){cout << "key = " << it->first << " value = " << it->second << endl;}
}int main()
{test();system("pause");return 0;
}