/**
 * Represents a double-ended queue (deque) data structure.
 * @template T The type of elements in the deque.
 */
export declare class Deque<T> {
    private items;
    /**
     * Adds an item to the front of the deque.
     * @param {T} item - The item to add to the front.
     */
    addFront(item: T): void;
    /**
     * Adds an item to the back of the deque.
     * @param {T} item - The item to add to the back.
     */
    addBack(item: T): void;
    /**
     * Removes and returns the item from the front of the deque.
     * @returns {T | undefined} The item removed from the front, or undefined if empty.
     */
    removeFront(): T | undefined;
    /**
     * Removes and returns the item from the back of the deque.
     * @returns {T | undefined} The item removed from the back, or undefined if empty.
     */
    removeBack(): T | undefined;
    /**
     * Returns the item at the front of the deque without removing it.
     * @returns {T | undefined} The item at the front, or undefined if empty.
     */
    peekFront(): T | undefined;
    /**
     * Returns the item at the back of the deque without removing it.
     * @returns {T | undefined} The item at the back, or undefined if empty.
     */
    peekBack(): T | undefined;
    /**
     * Checks if the deque is empty.
     * @returns {boolean} True if the deque is empty, false otherwise.
     */
    isEmpty(): boolean;
    /**
     * Returns the number of items in the deque.
     * @returns {number} The size of the deque.
     */
    size(): number;
}