pub struct Solution;
剑指 Offer 24. 反转链表 https://leetcode.cn/problems/fan-zhuan-lian-biao-lcof/
TypeId
self
Returns the argument unchanged.
Calls U::from(self).
U::from(self)
That is, this conversion is whatever the implementation of From<T> for U chooses to do.
From<T> for U