How to Remove Elements from a Vector while Iterating Without Invalidating Iterators?

Removing Elements from a Vector while Iterating

When iterating over a std::vector and deleting elements based on specific criteria, the use of multiple vectors or invalidated iterators can arise. This can be addressed by leveraging a more suitable data structure or employing an alternative approach.

Alternative Data Structures

Instead of using multiple vectors, consider utilizing alternative data structures such as:

• std::set: Maintains a collection of unique elements that are automatically sorted. This property can be advantageous for accessing elements in a specific order while avoiding duplicates.
• std::list: A doubly linked list allows for efficient insertion and deletion operations. Iterators remain valid after element removal, making it suitable for scenarios where the sequence of elements changes frequently.

Modified Approach

If using a different data structure is not feasible, there are workarounds within the std::vector:

1. Use an iterator-based approach: Iterate through the vector using a loop and call erase() on the iterator pointing to the element to be removed. This approach can be efficient if the number of elements to be removed is relatively small.
2. Use a vector-based approach: Iterate through the vector twice. In the first iteration, identify the elements to be removed and store their indices in a separate vector. In the second iteration, use the indices to erase the elements. This approach can be efficient if a large number of elements need to be removed.

By implementing these alternative methods, it's possible to remove elements from a std::vector while iterating efficiently and without invalidating iterators.

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