DFS
acwing165小猫爬山 https://www.acwing.com/problem/content/description/167/
poj2386Lake Countinghttp://poj.org/showsource?solution_id=20488890
poj1979Red and Blackhttp://poj.org/showsource?solution_id=20528070
poj3009Curling 2.0http://poj.org/showsource?solution_id=20528545