pub struct Solution;
剑指 Offer 63. 股票的最大利润 https://leetcode.cn/problems/gu-piao-de-zui-da-li-run-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