Removal Algorithms

Remove and Erase in std::deque

How do I remove elements from a std::deque using the remove-erase idiom?

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The std::deque (double-ended queue) container in C++ allows efficient insertions and deletions at both ends.

To remove elements from a std::deque using the remove-erase idiom, you follow a similar approach as with std::vector.

Here's an example to remove all occurrences of the number 3 from a std::deque:

#include <algorithm>
#include <deque>
#include <iostream>

int main() {
  std::deque<int> Source{1, 2, 3, 4, 5, 3, 6};

  // Step 1: Apply std::remove
  auto NewEnd = std::remove(
    Source.begin(), Source.end(), 3);

  // Step 2: Erase surplus elements
  Source.erase(NewEnd, Source.end());

  // Display the result
  std::cout << "Objects in Source: ";
  for (auto Num : Source) {
    std::cout << Num << ", ";
  }
}
Objects in Source: 1, 2, 4, 5, 6,

In this example:

  • std::remove() shifts the elements to be removed (the number 3) to the end of the std::deque.
  • The erase() method then removes these surplus elements, resizing the container accordingly.

Removing Elements Based on a Condition

You can also remove elements based on a condition using std::remove_if(). Here's how you can remove all even numbers from a std::deque:

#include <algorithm>
#include <deque>
#include <iostream>

int main() {
  std::deque<int> Source{1, 2, 3, 4, 5, 6};

  // Step 1: Apply std::remove_if
  auto NewEnd = std::remove_if(
    Source.begin(), Source.end(),
    [](int x) { return x % 2 == 0; }
  );

  // Step 2: Erase surplus elements
  Source.erase(NewEnd, Source.end());

  // Display the result
  std::cout << "Objects in Source: ";
  for (auto Num : Source) {
    std::cout << Num << ", ";
  }
}
Objects in Source: 1, 3, 5,

In this example:

  • We use std::remove_if() with a lambda function as the predicate to remove even numbers.
  • std::remove_if() moves the elements to be removed to the end of the std::deque.
  • The erase() method is then used to remove the surplus elements and adjust the container's size.

Using the remove-erase idiom with std::deque ensures efficient removal of elements and proper resizing of the container. This approach can be adapted to various conditions and element types, providing a flexible solution for container management.

Answers to questions are automatically generated and may not have been reviewed.

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