C++中set/multiset与map/multimap的使用详解

#include <iostream>
#include <set>
 
int main ()
{
  std::set<int> myset;
 
  // set some initial values:
  for (int i=1; i<5; ++i) myset.insert(i*3);    // set: 3 6 9 12
 
  for (int i=0; i<10; ++i)
  {
    std::cout << i;
    if (myset.count(i)!=0)
      std::cout << " is an element of myset.\n";
    else
      std::cout << " is not an element of myset.\n";
  }
 
  return 0;
}

#include <iostream>
#include <map>
 
int main ()
{
  std::map<char,int> mymap;
  std::map<char,int>::iterator itlow,itup;
 
  mymap['a']=20;
  mymap['b']=40;
  mymap['c']=60;
  mymap['d']=80;
  mymap['e']=100;
 
  itlow=mymap.lower_bound ('b');  // itlow points to b
  itup=mymap.upper_bound ('d');   // itup points to e (not d!)
 
  mymap.erase(itlow,itup);        // a => 20  e => 100
 
  // print content:
  for (std::map<char,int>::iterator it=mymap.begin(); it!=mymap.end(); ++it)
    std::cout << it->first << " => " << it->second << '\n';
 
  return 0;
}

template <class T1, class T2>
struct pair
{
	typedef T1 first_type;
	typedef T2 second_type;
	T1 first;
	T2 second;
	pair(): first(T1()), second(T2())
	{}
	pair(const T1& a, const T2& b): first(a), second(b)
	{}
};

template <class T1,class T2>
pair<T1,T2> make_pair (T1 x, T2 y)
{
	return ( pair<T1,T2>(x,y) );
}

Value& operator[] (const Key& k)
{
	pair<iterator,bool> ret=insert(make_pair(k,Value() ) );
	//在结构体pair中找到first(一个map的迭代器)，->解引用找到该迭代器的pair，再找该pair的second(即value)
	return ret.first->second;
}
//map的insert
pair<iterator,bool> insert (const value_type& pair);
//插入
dict["迭代器"];//在dict中找不到"迭代器"这个key，将新增一个节点，该节点的key为"迭代器",value为value类型的默认构造
//修改
dict["迭代器"]="iterator";//将key为"迭代器"的节点的value修改为"iterator"

struct Compare
{
    bool operator()(const pair<int,string>& a,const pair<int,string>& b)
    {
        return a.first>b.first || (a.first==b.first&&a.second<b.second);
    }
};
class Solution {
public:
    vector<string> topKFrequent(vector<string>& words, int k) {
        vector<string> ret;
        map<string,int> dataMap;
        for(const auto& str : words)
        {
            dataMap[str]++;
        }
        vector<pair<int,string>> v;
        for(auto& kv : dataMap)
        {
            v.push_back(make_pair(kv.second,kv.first));//dataMap的first是string，second是int
        }
        sort(v.begin(),v.end(),Compare());
        for(int i=0;i<k;++i)
        {
            ret.push_back(v[i].second);
        }
        return ret;
    }
};

class Solution {
public:
    vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
        set<int> s1(nums1.begin(),nums1.end());//nums1排序+去重    
        set<int> s2(nums2.begin(),nums2.end());//nums2排序+去重
        vector<int> ret;
        for(auto& e : s1)
        {
            if(s2.find(e)!=s2.end())
            {
                ret.push_back(e);
            }
        }
        return ret;
    }
};