TikTok Software Engineer Internship interview questions

there are 5 coding problems in OA, it requires me to finish them in 120 mins, but there is no time limitation for every single question. The first two questions are easy, even can be sovled using one line code, third and fourth are both medium, the last is a hard question

First, the interviewer introduced himself and then he asked me to quickly to introduce myself. Then we began to write code. Asked an algorithm question, which is how to sort the flags.