data-structure-algebra/doubly-linked-list

import assert from 'assert';

import Node from './Node.js';
import _rotate_left_unknown_length from './_rotate_left_unknown_length.js';
import _rotate_right_unknown_length from './_rotate_right_unknown_length.js';

/**
 * Do nothing if x is empty or n is zero.
 * Rotate right n steps if n is positive.
 * Rotate left n steps if n is negative.
 *
 * @param {Node} x The current first node.
 * @param {Node} z The current last node.
 * @param {number} n
 * @return {[Node, Node]} The new first and last node.
 */
export default function rotate_right(x, z, n) {
    assert(Number.isInteger(n));
    if (x === z) {
        // NOTE This takes care of x === null => z === null.
        return [x, z];
    }

    assert(x instanceof Node);
    assert(z instanceof Node);
    return n === 0
        ? [x, z]
        : n > 0
            ? _rotate_right_unknown_length(x, z, n)
            : _rotate_left_unknown_length(x, z, -n);
}