Showing posts with label Graphs. Show all posts
Showing posts with label Graphs. Show all posts

Wednesday, November 28, 2012

SPOJ PARADOX

Link : PARADOX

Category : Graphs


Hint : constructed an appropriate graph and do a depth-first traversal.


Solution : Consider this as a directed graph, with edge from vertex A to vertex B if statement A tells about statement B. Make list of incoming and outgoing edges for each vertex, and then do simple depth-first traversal on both, incoming and outgoing edges. If a statement claims opposite of the truth value assigned to an already visited node, then there is a paradox.


Note that for the traversal, the starting vertex can be anyone, and its truth value can be anything (true or false, because if truth value of one statement is changed, then truth value of all nodes reachable by it via directed/directing edges also gets flipped, hence preserving the PARADOX or NOT PARADOX answer.


Code: