https://loj.ac/p/x x = (6000-6015, 6121-6122, 6223-6227)
https://www.luogu.com.cn/problem/P2216
清华大学操作系统课程
二分答案的几种情况
https://ac.nowcoder.com/acm/contest/33192/J
https://ac.nowcoder.com/acm/contest/33189/A
https://codeforces.com/gym/104053/problem/M
https://ac.nowcoder.com/acm/contest/38727/L
https://acm.hdu.edu.cn/showproblem.php?pid=7191
https://ac.nowcoder.com/acm/contest/38727/B
