C : pancake
Diff : V-Hard->HELL(8->INF)
Comment :
Before : How to filp them by some rules?
Later : WHAT THE It doesn’t have a pattern.
In the end of the contest : I give up.
After : WHAT THE radix-3 number? turn to radix-10 number? BFS? AHHHHHHHHHHHHHHHHHHHHHHHHHHHHH, WHY IS THIS BFS?