hashset in c++

#include <iostream> 
#include <iterator> 
#include <map> 
  
using namespace std; 
  
int main() 
{ 
  
    // empty map container 
    map<int, int> gquiz1; 
  
    // insert elements in random order 
    gquiz1.insert(pair<int, int>(1, 40)); 
    gquiz1.insert(pair<int, int>(2, 30)); 
    gquiz1.insert(pair<int, int>(3, 60)); 
    gquiz1.insert(pair<int, int>(4, 20)); 
    gquiz1.insert(pair<int, int>(5, 50)); 
    gquiz1.insert(pair<int, int>(6, 50)); 
    gquiz1.insert(pair<int, int>(7, 10)); 
  
    // printing map gquiz1 
    map<int, int>::iterator itr; 
    cout << "\nThe map gquiz1 is : \n"; 
    cout << "\tKEY\tELEMENT\n"; 
    for (itr = gquiz1.begin(); itr != gquiz1.end(); ++itr) { 
        cout << '\t' << itr->first 
             << '\t' << itr->second << '\n'; 
    } 
    cout << endl; 
  
    // assigning the elements from gquiz1 to gquiz2 
    map<int, int> gquiz2(gquiz1.begin(), gquiz1.end()); 
  
    // print all elements of the map gquiz2 
    cout << "\nThe map gquiz2 after"
         << " assign from gquiz1 is : \n"; 
    cout << "\tKEY\tELEMENT\n"; 
    for (itr = gquiz2.begin(); itr != gquiz2.end(); ++itr) { 
        cout << '\t' << itr->first 
             << '\t' << itr->second << '\n'; 
    } 
    cout << endl; 
  
    // remove all elements up to 
    // element with key=3 in gquiz2 
    cout << "\ngquiz2 after removal of"
            " elements less than key=3 : \n"; 
    cout << "\tKEY\tELEMENT\n"; 
    gquiz2.erase(gquiz2.begin(), gquiz2.find(3)); 
    for (itr = gquiz2.begin(); itr != gquiz2.end(); ++itr) { 
        cout << '\t' << itr->first 
             << '\t' << itr->second << '\n'; 
    } 
  
    // remove all elements with key = 4 
    int num; 
    num = gquiz2.erase(4); 
    cout << "\ngquiz2.erase(4) : "; 
    cout << num << " removed \n"; 
    cout << "\tKEY\tELEMENT\n"; 
    for (itr = gquiz2.begin(); itr != gquiz2.end(); ++itr) { 
        cout << '\t' << itr->first 
             << '\t' << itr->second << '\n'; 
    } 
  
    cout << endl; 
  
    // lower bound and upper bound for map gquiz1 key = 5 
    cout << "gquiz1.lower_bound(5) : "
         << "\tKEY = "; 
    cout << gquiz1.lower_bound(5)->first << '\t'; 
    cout << "\tELEMENT = "
         << gquiz1.lower_bound(5)->second << endl; 
    cout << "gquiz1.upper_bound(5) : "
         << "\tKEY = "; 
    cout << gquiz1.upper_bound(5)->first << '\t'; 
    cout << "\tELEMENT = "
         << gquiz1.upper_bound(5)->second << endl; 
  
    return 0; 
} 

#include <bitset> 
  
// functional header 
// for hash<class template> class 
#include <functional> 
  
#include <iostream> 
#include <string> 
#include <vector> 
  
using namespace std; 
  
// To demonstrate String Hashing 
void stringHashing() 
{ 
  
    // Get the string 
    // to get its hash value 
    string hashing1 = "Geeks"; 
  
    // Instatiation of Object 
    hash<string> mystdhash; 
  
    // Using operator() to get hash value 
    cout << "String hash values: "
         << mystdhash(hashing1) 
         << endl; 
} 
  
// To demonstrate BITSET Hashing 
void bitsetHashing() 
{ 
  
    // Get the BITSET 
    // to get its hash value 
    bitset<5> h_bitset("10101"); 
  
    // Instatiation of Object 
    hash<bitset<5> > hash_bitset; 
  
    // Using operator() to get hash value 
    cout << "\nBitset 10101 hash value: "
         << hash_bitset(h_bitset) << endl; 
} 
  
// To demonstrate Vector<bool> Hashing 
void vectorHashing() 
{ 
  
    // Get the Vector<bool> 
    // to get its hash value 
    vector<bool> 
        h_vecbool{ true, false, 
                   true, false }; 
  
    // Instatiation of Object 
    hash<vector<bool> > hash_vector_bool; 
  
    // Using operator() to get hash value 
    cout << "\nVector<bool> hash value: "
         << hash_vector_bool(h_vecbool) 
         << endl; 
} 
  
// To demonstrate Char Hashing 
void charHashing() 
{ 
  
    // Get the char 
    // to get its hash value 
    char ch = 'a'; 
  
    // Instatiation of Object 
    hash<char> hash_char; 
  
    // Using operator() to get hash value 
    cout << "\nChar hash values: "
         << hash_char(ch) 
         << endl; 
} 
  
// Driver Code 
int main() 
{ 
  
    stringHashing(); 
    bitsetHashing(); 
    vectorHashing(); 
    charHashing(); 
} 

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