Deque

A deque (double-ended queue) in C++ is a sequence container that allows adding and removing elements from both the front and back efficiently. Unlike a vector, which only allows fast insertions and deletions at the back, a deque provides constant time complexity for insertions and deletions at both ends. This is useful for scenarios like implementing queues, stacks, or sliding window algorithms.

Syntax

std::deque<datatype> name;

• datatype: The type of elements the deque will hold (e.g., int, float, string, etc.).
• name: The name of the deque.

Example

The following code inserts elements (13 & 8) at the front and back and access them.

#include <deque>
#include <iostream>

int main() {
  std::deque<int> myDeque;  // Declare a deque of integers

  myDeque.push_back(13);    // Insert element at the back
  myDeque.push_front(8);    // Insert element at the front

  std::cout << "Front: " << myDeque.front() << std::endl;
  std::cout << "Back: " << myDeque.back() << std::endl;

  return 0;
}

The output of the above program will be:

Front: 8
Back: 13

Equivalent Methods in Stack, Queue, and Deque