Bessie has gotten herself stuck on the wrong side of Farmer John's barn again, and since her vision
is so poor, she needs your help navigating across the barn.The barn is described by an N×N grid of
square cells (2≤N≤20), some being empty and some containing impassable haybales. Bessie starts in
the lower-left corner (cell 1,1) and wants to move to the upper-right corner (cell N,N). You can gui
de her by telling her a sequence of instructions, each of which is either "forward", "turn left 90 d
egrees", or "turn right 90 degrees". You want to issue the shortest sequence of instructions that wi
ll guide her to her destination. If you instruct Bessie to move off the grid (i.e., into the barn wa
ll) or into a haybale, she will not move and will skip to the next command in your sequence.Unfortun
ately, Bessie doesn't know if she starts out facing up (towards cell 1,2) or right (towards cell 2,1
). You need to give the shortest sequence of directions that will guide her to the goal regardless o
f which case is true. Once she reaches the goal she will ignore further commands.
给定一个N*N的网格(N<=20)，你从左下角出发，要到达右上角，网格中会有障碍物你要给定一个长度最短的行为序
列（往前走，左转，右转），使得无论Bessie处于左下角时是头朝向上还是朝向左都可以在执行完这个序列后到达
右上角如果当前的行为会导致Bessie走到障碍物上或者越界，则Bessie会忽视这个行为
