http://usaco.org/index.php?page=viewproblem2&cpid=360

Please tell me how to solve this.I am stuck.I think I am not also getting what the question wants to ask.

http://usaco.org/index.php?page=viewproblem2&cpid=360

Please tell me how to solve this.I am stuck.I think I am not also getting what the question wants to ask.

The question essentially asks you to find the number of distinct pairing of wormholes such that there is a position on the map which leads to Bessie getting trapped when she starts moving in the +x direction from that position.

Two pairings are different if at least one wormhole is paired with a different wormhole in the two pairings. Looking at the constraints, you can tell that brute force must be possible.

Total number of distinct pairings can be calculated to check:

(12C2 * 10C2 * 8C2 * 6C2 * 4C2 * 2C2 ) / 6! = 11 * 9 * 7 * 5 * 3 *1 = 10395.

For each pairing, you can check by running a modified DFS if there is a cycle in the graph described by the pairing. You would have to add edges between wormholes with the same y-coordinate, the edge going from the left wormhole(one with lesser value of x-coordinate) to the right one(one with greater value of x-coordinate).

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Thank u sikander_nsit