# P2864 [USACO06JAN]树林The Grove

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• 240提交
• 题目提供者 FarmerJohn2
• 评测方式 云端评测
• 标签 广度优先搜索,BFS USACO 2006 高性能
• 难度 提高+/省选-
• 时空限制 1000ms / 128MB
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## 题目描述

The pasture contains a small, contiguous grove of trees that has no 'holes' in the middle of the it. Bessie wonders: how far is it to walk around that grove and get back to my starting position? She's just sure there is a way to do it by going from her start location to successive locations by walking horizontally, vertically, or diagonally and counting each move as a single step. Just looking at it, she doesn't think you could pass 'through' the grove on a tricky diagonal. Your job is to calculate the minimum number of steps she must take.

Happily, Bessie lives on a simple world where the pasture is represented by a grid with R rows and C columns (1 <= R <= 50, 1 <= C <= 50). Here's a typical example where '.' is pasture (which Bessie may traverse), 'X' is the grove of trees, '*' represents Bessie's start and end position, and '+' marks one shortest path she can walk to circumnavigate the grove (i.e., the answer):

...+...
..+X+..
.+XXX+.
..+XXX+
..+X..+
...+++*

The path shown is not the only possible shortest path; Bessie might have taken a diagonal step from her start position and achieved a similar length solution. Bessie is happy that she's starting 'outside' the grove instead of in a sort of 'harbor' that could complicate finding the best path.

牧场里有一片树林，林子里没有坑.

贝茜很想知道，最少需要多少步能围绕树林走一圈，最后回到起点.她能上下左右走，也能 走对角线格子.

牧场被分成R行C列(1 <= R =< 50，1 < =C<= 50).下面是一张样例的地图，其中表示贝茜 可以走的空地，“X”表示树林，表示起点.而贝茜走的最近的路已经特别地用“ + ”表示 出来.

题目保证，最短的路径一定可以找到.

## 输入输出格式

输入格式：

Line 1: Two space-separated integers: R and C

Lines 2..R+1: Line i+1 describes row i with C characters (with no spaces between them).

输出格式：

Line 1: The single line contains a single integer which is the smallest number of steps required to circumnavigate the grove.

## 输入输出样例

输入样例#1： 复制
6 7
.......
...X...
..XXX..
...XXX.
...X...
......*
输出样例#1： 复制
13
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