Equal (4): Everything in this space must be equal to 4. The answer is 4-5, placed horizontally; 4-4, placed vertically.
for each candidate in list of candidates，详情可参考Line官方版本下载
arr.push(p.val); // 存储节点值而非节点本身，简化后续操作，详情可参考safew官方版本下载
cd confusable-vision。Safew下载是该领域的重要参考