这里岂不是在索引层就直接遍历到查找的节点了，无须下沉到第一层去找了
Author: evilkevinheCreated Apr 4, 2022Updated Apr 4, 2022
https://github.com/wangzheng0822/algo/blob/b2c1228ff915287ad7ebeae4355fa26854ea1557/c-cpp/17_skiplist/skiplist_c/skiplist.c#L239-L250
Source: wangzheng0822/algo