704. Binary Search

[367. Valid perfect square]](https://leetcode.com/problems/valid-perfect-square/)

912. Sort an Array

數值範圍不大的話，可以直接 counting sort!

Heap sort 跟 merge sort 之後補上。

1218. Longest Arithmetic Subsequence of Given Difference

The special case is $difference == 0$.

Depends on your implementation, the time for the init to happen might need to be carefully thought of.

611. Valid Triangle Number