1784 - [Usaco2010 Jan]island

一个字符矩阵，'.'为海洋，'A'为主岛，'x'为其它岛，保证所有'A'构成一个联通块，画一个圈，使得所有的'A'在圈内，所有的'x'在圈外，更具体的看样例，求这样的圈的最小周长

Line 1: Two space-separated integers: H and W * Lines 2..H+1: Line i+1 contains contains W characters that are the elements of map row i (all '.' or 'x' or 'A')

• Line 1: The minimum length of a path that Farmer John's cruise ship can take