这题就是一个裸的BFS，luogu的翻译不好，建议看原文QAQ const z:array[1..4,1..2]of -1..1=((1,0),(0,1),(-1,0),(0,-1));var i,j,k:longint;m,n,h,t:longint;ch:char;a,b:array[0..601,0..601]of boolean;x,y:array[0..1000000]of long