pub struct Solution;
剑指 Offer 03. 数组中重复的数字 https://leetcode.cn/problems/shu-zu-zhong-zhong-fu-de-shu-zi-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