蓝桥杯题单day1
（按顺序）
bfs + dfs
https://www.luogu.com.cn/problem/P1162
https://www.luogu.com.cn/problem/P1378
https://www.luogu.com.cn/problem/P8644
https://www.lanqiao.cn/problems/280/learning/
二分
https://www.luogu.com.cn/problem/P8647
https://www.luogu.com.cn/problem/AT_abc144_e