ROBOTGRI  Robots on a grid
You have recently made a grid traversing robot that can
nd its way from the top left corner of a grid to the
bottom right corner. However, you had forgotten all your
AI programming skills, so you only programmed your robot
to go rightwards and downwards (that's after all where the
goal is). You have placed your robot on a grid with some
obstacles, and you sit and observe. However, after a while
you get tired of observing it getting stuck, and ask yourself
\How many paths are there from the start position to the
goal position?", and \If there are none, could the robot have
made it to the goal if it could walk upwards and leftwards?"
So you decide to write a program that, given a grid of
size n x n with some obstacles marked on it where the robot
cannot walk, counts the dierent ways the robot could go
from the top left corner s to the bottom right t, and if none,
tests if it were possible if it could walk up and left as well.
However, your program does not handle very large numbers, so the answer should be
given modulo 2^31  1.
Input
On the rst line is one integer, 1 < n <= 1000. Then follows n lines, each with n characters,
where each character is one of '.' and '#', where '.' is to be interpreted as a walkable
tile and '#' as a nonwalkable tile. There will never be a wall at s, and there will never
be a wall at t.
Output
Output one line with the number of dierent paths starting in s and ending in t (modulo
2^31  1) or THE GAME IS A LIE if you cannot go from s to t going only rightwards and
downwards but you can if you are allowed to go left and up as well, or INCONCEIVABLE if
there simply is no path from s to t.
Example
Input: 5
.....
#..#.
#..#.
...#.
..... Output: 6
hide comments
jenishmonpara:
20200420 15:35:48
My first AC in one go in SPOJ.


nagaraj41:
20200413 08:38:54
just google 2^31 1 and copy paste if you are having issues. Also take care of the output format. i typed "THIS" instead of "THE" resulting in WA's. felt foolish. 

coolio_1:
20200219 17:16:39
Multiple WA due to MOD.


pas7582128:
20191230 19:06:44
AC in one go. 

sudhiawasthi:
20191114 11:10:24
For people getting WA on test case 18, check how your bfs works for the first row and first column, the invalid moves are causing WA. 

wingman__7:
20191109 18:09:41
easy BFS problem, use queue no need for recursion 

ekta_9:
20191109 07:24:47
i am using top down dp here but still getting TLE .whyyyyy? 

darshanpatel:
20190522 07:29:26
You have to actually print "THE GAME IS A LIE " or " INCONCEIVABLE" (without quotes) ! Take care of modulo by typecasting 1<<31 to ((long long)1<<31). 

sky_scraper:
20190512 14:29:29
Damn the modulo just gave me a headache use (1ll<<31)1 instead of ll(1<<31)  1 and here "ll" == long long 

vengatesh15:
20170325 09:23:46
dfs tle .. bfs AC.. 
Added by:  Krzysztof Lewko 
Date:  20111005 
Time limit:  1s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ASM64 
Resource:  Nordic programming contest 