Erase-remove idiom

The erase-remove idiom is a common C++ technique to efficiently remove elements from a container, particularly from standard sequence containers like std::vector, std::list, and std::deque. It leverages the standard library algorithms std::remove (or std::remove_if) and the member function erase().

The idiom consists of two steps:

• std::remove (or std::remove_if) moves the elements to be removed towards the end of the container and returns an iterator pointing to the first element to remove.
• container.erase() removes the elements from the container using the iterator obtained in the previous step.

Here's an example:

#include <algorithm>
#include <vector>
#include <iostream>

int main() {
    std::vector<int> numbers = {1, 3, 2, 4, 3, 5, 3};
    
    // Remove all occurrences of 3 from the vector.
    numbers.erase(std::remove(numbers.begin(), numbers.end(), 3), numbers.end());

    for (int number : numbers) {
        std::cout << number << " ";
    }

    return 0;
}

Output:

1 2 4 5

In this example, we used the std::remove algorithm to remove all occurrences of the number 3 from the std::vector<int> numbers. After the removal, the vector contains only 1, 2, 4, and 5, as the output shows.