CODEWITHSUNDEEP
c#algorithmgraphpath
Cemre Mengü
Cemre Mengü

Reputation: 18754

Finding the path from a list of adjacency information

I have data in database which is in the form of:

A -> B
C -> D
B -> C
F -> G
G -> J
X -> Z

This basically means that A goes to B, C goes to D etc. Given this data and a node (such as C) I would like to construct the complete path that C is found that is A -> B -> C -> D . I tried to do this by using a few dictionaries and recursive loops but I don't like such a sluggish solution since there are lots of data in db. What is a better way to solve this problem ? In terms of both algorithm and the data structure ? Any ideas or hints are appreciated.

Upvotes: 1

Views: 144

Answers (1)

amit
amit

Reputation: 178411

You are looking basically for DFS, but you need to do it twice - one per direction.

First do a a DFS on the reverse 'graph', starting from C.
In your example it will give you Path1 = C->B->A

Next, do a DFS on the original graph, again from C.
In your example it will give you Path2= C->D

Now, by reversing Path1, and concatinating Path2 to it you will get:

reverse(Path1)  + Path2 = A->B->C + C->D = A->B->C->D

Clarification - DFS is just abstraction, what you actually are doing is something similar to (pseudo code):

current <- C
list = []
while (current != null):
   list.addFirst(current)
   current <- u such that (u,current) is in the DataBase
current <- C
list.deleteLast() // last is C
while (current != null):
   list.addLast(current)
   current <- u such that (current,u) is in the DataBase

Note that finding u both cases is a simple dictionary look up, in the first the "Target" is the key, and in the second the "Source" is the key.

Upvotes: 2

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