Can you use map and set???

一、map和set的引入

        我们都知道，STL在C++ 中得到了广泛使用，它不仅仅由于是提供了类似vector,list等方便使用的容器，更是因为它封装了许多复杂的数据结构算法和大量数据结构的操作。vector封装数组，list封装链表，而map和set则是用来封装二叉树的。

        还有要知道的就说STL中的容器分为两大类：序列式容器和关联式容器，其中vector和list属于序列式容器，而map和set则属于关联式容器，那么为什么map和set的插入删除效率比其他序列式容器高呢？原因就是关联式容器不需要进行内存拷贝和内存移动，所有元素都是以节点的方式进行存储的，插入删除自然更高效。

二、map在库中的基础知识

1、map的模板参数：

2、常用接口：

3、map运用的例子：统计水果出现的次数以及前K种出现次数最多的水果

#include <iostream>#include <set>#include <map>#include <algorithm>#include <string>#include <vector>using namespace std;template <typename K,typename V>void sortMap(string fruits[],size_t sz,const map<K,V> &m)//统计出现最多的前k种水果（降序）{map <string,int> count;for (size_t i = 0; i < sz; ++i){count[fruits[i]]++;}//将迭代器导入vectorvector<map<string,int>::iterator> heap;map<string,int>::iterator mapIt = count.begin();while(mapIt != count.end()){heap.push_back(mapIt);++mapIt;}//建小堆struct Com{bool operator()(const map<string,int>::iterator l,const map<string,int>::iterator r){return l->second < r->second;}};sort(heap.begin(),heap.end(),Com());//make_heap(heap.begin(),heap.end(),Com());//int diff = heap.size() - k;////向下调整//while(diff--)//{//pop_heap(heap.begin(),heap.end(),Com());//heap.pop_back();//}//输出结果while(heap.size() != 0){cout<<heap.back()->first<<":"<<heap.back()->second<<endl;heap.pop_back();}}void CountMap(string fruits[],size_t sz)//统计水果出现的次数{map <string,int> count;for (size_t i = 0; i < sz; ++i){    ////方法1//map <string,int>::iterator it = count.find(fruits[i]);//if (it != count.end())//{//it->second++;////*(it).second++;//}//else//{//count.insert(pair<string,int>(fruits[i],1));//}////方法2//pair <map<string,int>::iterator,bool> ret;//ret = count.insert(pair<string,int>(fruits[i],1));//if (ret.second == false)//{//ret.first->second++;//}//方法3count[fruits[i]]++;}}int main(){map <string,int> count;string fruits[] = {"apple","banana","orange","pineapple","grape","banana","orange","apple","apple","orange","pineapple","grape","orange","pineapple","pear","grapefruit","mango","mango juice","apple","Hami melon","melon","peach","banana","pineapple","grape","orange","pineapple","pear","grapefruit","mango","apple","melon","peach","banana","melon","peach","banana", "Hami melon","pineapple","grape","orange","pineapple","pear","grapefruit","mango","peach","peach"};size_t sz = sizeof(fruits)/sizeof(fruits[0]);CountMap(fruits,sz);sortMap(fruits,sz,count);system("pause");return 0;}

统计水果出现次数的过程截图：

运行结果：

三、set在库中的基本内容

1、set的模板参数

2、常用接口

3、set运用实例

set的插入和删除：

代码运用：

void PrintSet(const set<int>& s){set <int>::iterator it = s.begin();while (it != s.end()){cout<<*it<<" ";it++;}cout<<endl;}void TestSet(){set <int> s;//1普通插入，返回pair类型pair<set<int>::iterator,bool> ret;ret = s.insert(2);if (ret.second == true){cout<<"插入成功!"<<endl;}else{cout<<"插入的值已存在，插入失败！"<<endl;}ret = s.insert(4);if (ret.second == true){cout<<"插入成功!"<<endl;}else{cout<<"插入的值已存在，插入失败！"<<endl;}ret = s.insert(2);if (ret.second == true){cout<<"插入成功!"<<endl;}else{cout<<"插入的值已存在，插入失败！"<<endl;}PrintSet(s);//2、根据迭代器位置进行插入，返回一个迭代器set<int>::iterator it = s.find(2);set<int>::iterator retIt = s.insert(it,3);if (retIt == s.end()){cout<<"插入的值已存在，插入失败"<<endl;}else{cout<<"插入成功!"<<endl;}retIt = s.insert(it,4);if (retIt == s.end()){cout<<"插入的值已存在，插入失败"<<endl;}else{cout<<"插入成功!"<<endl;}PrintSet(s);//3、插入一段迭代器区间，无返回值vector<int> v;v.push_back(5);v.push_back(6);v.push_back(7);vector<int>::iterator start = v.begin();vector<int>::iterator tail = v.end();s.insert(start,tail);PrintSet(s);//set的删除s.insert(0);s.insert(1);s.insert(2);s.insert(3);s.insert(4);s.insert(5);PrintSet(s);//1.通过迭代器位置删除,无返回值set<int>::iterator eraseIt = s.find(0);s.erase(eraseIt);PrintSet(s);//2.通过值删除,删除成功返回1,不存在返回0size_t a = s.erase(0);PrintSet(s);//3.删除迭代器区间,无返回值s.erase(++s.begin(),--s.end());//只留下第一个和最后一个,其余全部删除PrintSet(s);}int main(){TestSet();system("pause");return 0;}

运行结果：