LABYR1  Labyrinth
The northern part of the Pyramid contains a very large and complicated labyrinth. The labyrinth is divided into square blocks, each of them either filled by rock, or free. There is also a little hook on the floor in the center of every free block. The ACM have found that two of the hooks must be connected by a rope that runs through the hooks in every block on the path between the connected ones. When the rope is fastened, a secret door opens. The problem is that we do not know which hooks to connect. That means also that the neccessary length of the rope is unknown. Your task is to determine the maximum length of the rope we could need for a given labyrinth.
Input
The input consists of T test cases. The number of them (T) is given on the first line of the input file.
Each test case begins with a line containing two integers C and R (3 <= C,R <= 1000) indicating the number of columns and rows. Then exactly R lines follow, each containing C characters. These characters specify the labyrinth. Each of them is either a hash mark (#
) or a period (.
). Hash marks represent rocks, periods are free blocks. It is possible to walk between neighbouring blocks only, where neighbouring blocks are blocks sharing a common side. We cannot walk diagonally and we cannot step out of the labyrinth.
The labyrinth is designed in such a way that there is exactly one path between any two free blocks. Consequently, if we find the proper hooks to connect, it is easy to find the right path connecting them.
Output
Your program must print exactly one line of output for each test case. The line must contain the sentence "Maximum rope length is X.
" where Xis the length of the longest path between any two free blocks, measured in blocks.
Example
Sample Input: 2 3 3 ### #.# ### 7 6 ####### #.#.### #.#.### #.#.#.# #.....# ####### Sample output: Maximum rope length is 0. Maximum rope length is 8.Warning: large Input/Output data, be careful with certain languages
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manishjoshi394:
20181125 18:17:23
Starting DFS randomly from some node will NOT work. 2 DFS are required. No use to visited array here, there is only 1 connected component.


joe85123:
20181104 17:29:49
pretty much the same solution with "the longest path in a tree"


mittalprashant:
20180810 19:42:23
This comment has been deleted by the user.


markomafko972:
20180719 17:44:28
Try CLCKBAIT after this! 

hello_world123:
20180613 16:22:03
Can be done using only DFS ..... But requires more thinking 

ultra_7:
20180102 09:31:03
input is C first and then R. dont miss this. 

aniket000:
20171230 06:37:23
took me 3 hours to debug but AC finally!! :) 

akash21391:
20171106 18:14:48
Last edit: 20171106 19:45:31 

bani_raheja:
20171020 23:16:56
AC in one go :) 

Omar:
20171016 01:43:29
make sure to read rows and column in the right way . 
Added by:  adrian 
Date:  20040606 
Time limit:  5s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All 
Resource:  ACM Central European Programming Contest, Prague 1999 