- 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
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.
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.