data-structure-algebra/doubly-linked-list

import assert from 'assert';

import Node from './Node.js';
import _concat from './_concat.js';

/**
 * Concatenate two input lists.
 *
 * @param {Node} x First node of first input list (can be null).
 * @param {Node} z Last node of first input list (can be null).
 * @param {Node} y First node of second input list (can be null).
 * @return {Node} First node of the output list (or null if empty).
 */
export default function concat(x, z, y) {
    if (x === null) {
        assert(z === null);
        return y;
    }

    assert(x instanceof Node);
    assert(z instanceof Node);
    if (y === null) return x;
    assert(y instanceof Node);
    _concat(z, y);
    return x;
}