vector<int>& res

A vector is a container class in C++ that represents a dynamic array. It is defined in the standard library header <vector> and is part of the STL (Standard Template Library).

A vector<int> is a vector that stores integer values. It can be used to store a sequence of integers that can be accessed using an index. Here is an example of how to create and use a vector<int>:

#include <vector>
#include <iostream>

int main() {
    std::vector<int> numbers = {1, 2, 3, 4, 5};

    // Accessing elements
    std::cout << numbers[0] << std::endl; // Output: 1

    // Iterating over elements
    for (auto num : numbers) {
        std::cout << num << " ";
    }
    // Output: 1 2 3 4 5

    // Adding elements
    numbers.push_back(6);

    // Removing elements
    numbers.pop_back();

    return 0;
}

In this example, we create a vector of integers called numbers and initialize it with some values. We then access elements using the [] operator and iterate over them using a for loop. We also demonstrate how to add and remove elements from the vector using the push_back() and pop_back() methods.