C++ unordered_map和unordered_set的使用示例详解

template<class Key,        //unoredered_set::key_type/value_type
        class Hash=hash<Key>,    //unoredered_set::hasher
        class Pred=equal_to<Key>,    //unoredered_set::key_equal
        class Alloc=allocator<Key>    //unoredered_set::allocator_type
        > class unordered_set;

pair<iterator,bool> insert(const value_type& val);
size_type erase(const key_type& k);
iterator find(const key_type& k);

int test_set(){
    const size_t N=1000000;
    unordered_set<int> us;
    set<int> s;
    vector<int> v;
    v.reserve(N);
    srand(time(0));
    for(size_t i=0;i<N;i++){
        //v.push_back(rand());    //N比较大时，重复值比较多
        v.push_back(rand()+i);    //重复值相对少
        //v.push_back(i);    //没有重复，有序
    }
    size_t begin1=clock();
    for(auto e:v)
        s.insert(e);
    size_t endl=clock();
    cout<<"set insert:"<<endl-begin1<<endl;
    size_t begin2=clock();
    for(auto e:v)
        us.insert(e);
    size_t end2=clock();
    cout<<"unordered_set insert:"<<end2-begin2<<endl;
    int m1=0;
    size_t begin3=clock();
    for(auto e:v){
        auto ret=s.find(e);
        if(ret!=s.end()){
            ++m1;
        }
    }
    size_t end3=clock();
    cout<<"set find:"<<end3-begin3<<"->"<<m1<<endl;
    int m2=0;
    size_t begin4=clock();
    for(auto e:v){
        auto ret=us.find(e);
        if(ret!=us.end()){
            ++m1;
        }
    }
    size_t end4=clock();
    cout<<"unordered_set find:"<<end4-begin4<<"->"<<m2<<endl;
    cout<<"插入数据个数："<<s.size()<<endl;
    cout<<"插入数据个数："<<us.size()<<endl;
    size_t begin5()=clock();
    for(auto e:v)
        s.erase(e);
    size_t end5=clock();
    cout<<"set erase:"<<end5-begin5<<endl;
    size_t begin6()=clock();
    for(auto e:v)
        us.erase(e);
    size_t end6=clock();
    cout<<"unordered_set erase:"<<end6-begin6<<endl;
    return 0;
}
int main(){
    test_set();
    return 0;
}

pair<iterator,bool> insert(const value_type& val);
size_type erase(const key_type& k);
iterator find(const key_type& k);
mapped_type& operator[](const key_type& k);