ABCPATH  ABC Path
You will be given a 2dimensional grid of letters. Find the length of the longest path of consecutive letters, starting at 'A'. Paths can step from one letter in the grid to any adjacent letter (horizontally, vertically, or diagonally).
For example, in the following grid, there are several paths from 'A' to 'D', but none from 'A' to 'E':
One such path is:
Input
Each test case will start with a line contains two integers H, W the height and width of the grid respectively 1 <= H, W <= 50. Then H lines follow each of W uppercase letters only. Input terminates with H = 0 and W = 0.
Output
For each test case print “Case C: X” without quotes where C is the case number starting with 1 and X is the solution.
Example
Sample Input: 4 3 ABE CFG BDH ABC 0 0 Sample Output: Case 1: 4
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god_father:
20130126 09:47:13
nice question...be carefull about visited paths it caused me 2 TLE; 

cegprakash:
20111115 05:46:57
is A to B, B to C, C to B, B to C, C to D is a valid path?


Ali Arous:
20111106 09:35:49
No, the Longest path is from "A" to "Z" 

[Retired] Fendy Kosnatha:
20111106 04:22:22
if after 'Z' can be back to 'A'?? 
Added by:  Ali Arous 
Date:  20111105 
Time limit:  1s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ASM64 
Resource:  FCIS Local Contest 2012 