KFSTB  Help the Commander in Chief
Help the Commander in Chief
The Country of byteland is in a state of war with its neighboring nation bitland which is a small island. The king of byteland needs to send his soldiers across the sea to attack bitland. It is not easy for bytelandian soldiers to cross the sea between the two countries as there are soldiers of bitland who are constantly on patrol.
But, The commander of byteland through his secret sources has gathered some information about the camping spots in between, It is as follows. There are C camping spots in the sea between the two countries. There are B one way bridges, each bridge is between two camps. Bytelandian army can use these bridges without any danger of being attacked. The commander also knows that if the army leaves a camping spot along a bridge safely it is not possible to return back safely to the same camping spot.
The camping spot closest to the bytelandian shore is S and the camping spot closest to the bitlandian shore is T. The commander in chief of byteland wants to formulate a strategy for the army to safely move from the camping spot S to T. You have been assigned the task of finding the number of possible paths that a soldier could follow from camping spot S to T.
Input
The first line of input contains the number of test cases D. For each test case the first line contains C, B, S and T number of camping spots, number of one way bridges, camping spot close to byteland and camping spot close to bitland respectively. The next B lines contain description of bridges. Each bridge is described on a single line by two integers X and Y denoting the starting and ending point of a bridge.
Output
In each line print the number of possible paths modulo 1000000007
Sample Input
2
4 4 1 4
1 2
1 3
2 4
3 4
5 5 1 5
1 2
2 3
2 4
3 5
4 5
Sample Output
2
2
Constraints
1<= D <= 10
1<= C <= 10000
1<= B <= 10000
1 <= X,Y <= C
1 <= S,T <= C
hide comments
dkkv0000:
20200122 19:11:44
easy peasy lemon squeezy 

its_himanshu:
20191213 12:58:02
Last edit: 20191213 12:58:25 

its_himanshu:
20191212 14:04:54
AC in one go....


wingman__7:
20191014 16:45:19
HInt:


nishanth4298:
20191009 16:25:25
If the graph is a DAG, then you cant even reach the same island again, wth!!The whole question needs to be modified


sumantopal07:
20190913 10:45:45
Dfs and maintain an array to store number of ways to reach destination


saurabh8522:
20190505 10:47:26
@samarth1402 can u please send ur solution i followed the same approach but i am getting tle


samarth1402:
20190323 13:44:46
Nice DP+bfs question.


jagadishsagi:
20180625 04:46:56
Dfs + dp AC in one go 

yogi10:
20180125 14:00:23
nice problem i simply thinking to the soln using dfs with some optimization give accepted *****

Added by:  rizwan hudda 
Date:  20120904 
Time limit:  1s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ASM64 
Resource:  Kodefest 2012 IITK  Own problem 