经典动态压缩DP，状态是f[i][j]，表示第i行，以3进制j为状态。j的位代表一个格子，只能是：0表示第i行和第i - 1行都没有炮兵，1表示第i行没有炮兵而第i-1行有炮兵，2表示第i行有炮兵-Classic dynamic compression DP, status is f[i][j], that the first line i to j for the 3-band status. j representatives of a lattice, can only be: 0 indicated that the first i rows and the first i- 1 line no artillery, the first one that i did not artillery line the first i-1 lines have artillery, line 2 that the first i have artillery