not1 and not2 function templates in C++ STL with Examples

// C++ program to demonstrate
// not1 function template

#include <bits/stdc++.h>
using namespace std;

struct pred {
    bool operator()(const int i) const
    {
        return (i % 2 == 0);
    }

    // defines argument_type for unary functor
    // it is begin used by not1
    // as argument_type
    typedef int argument_type;
};

// Driver code
int main()
{
    vector<int> odd{ 1, 2, 3, 4, 5,
                     6, 7, 8, 9, 10 };

    // simple pred functor use
    // it removes even numbers
    auto end
        = remove_if(odd.begin(),
                    odd.end(),
                    pred());

    odd.resize(distance(odd.begin(), end));

    cout << "removal of even elements: ";
    for (int i = 0; i < odd.size(); i++) {
        cout << odd[i] << " ";
    }
    cout << "\n";

    vector<int> even{ 1, 2, 3, 4, 5,
                      6, 7, 8, 9, 10 };

    // complement of pred using not1
    // which removes odd numbers
    end
        = remove_if(even.begin(),
                    even.end(),
                    not1(pred()));

    even.resize(distance(even.begin(), end));

    cout << "removal of odd elements: ";
    for (int i = 0; i < even.size(); i++) {
        cout << even[i] << " ";
    }

    return 0;
}

// C++ program to demonstrate
// not2 function template

#include <bits/stdc++.h>
using namespace std;

int main()
{
    vector<int> vec{ 4, 2, 7, 9, 3, 5, 10, 6 };

    // simple use of not2 just provide binary
    // functor and it will return it complement
    sort(vec.begin(), vec.end(), not2(less<int>()));

    for (int i = 0; i < vec.size(); i++) {
        cout << vec[i] << " ";
    }
    return 0;
}