There are two main types of smoke alarm tech, says Raman Chagger, principal consultant at BRE, the Building Research Establishment. Ionisation-based systems use a tiny amount of radioactive material to charge, or ionise, particles in the air which flow between two small plates. Should smoke interrupt that flow of charged particles, the alarm goes off.
3 transform chain
，这一点在雷电模拟器官方版本下载中也有详细论述
siftDown(arr, n, largest); // 递归下沉
（三）买卖或者使用伪造、变造的国家机关、人民团体、企业、事业单位或者其他组织的公文、证件、证明文件、印章的；
// 倒序遍历：从最后一个元素开始（核心思路！易错点1）