Boxer's blog

SCPC 14 Problem G
By Boxer, 12 years ago, In English

Hi everyone , i am trying to solve SCPC14 in gym and particulary i was thinking how to solve problem G i think a naive bruteforce with backtracking but it was very slow .

Can somebody give me some hints in order to solve this problem.

Thanks in advance.

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12 years ago, hide # |
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I think BFS will work, because there are not too many different board states.

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    12 years ago, hide # ^ |
     
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    Believe me that using bfs inside your backtracking and searching all board states it's so slow , must have some prunning or similar in this problem.

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      12 years ago, hide # ^ |
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      have you tried BFS and failed? the fact that number of different colors is only 4 and the cells are shifted to left and down makes number of states very low , also you can use previously computed states in many test cases in the same test file

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        12 years ago, hide # ^ |
         
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        In fact the sample input runs so slow . I think that the number of states it's huge.

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          12 years ago, hide # ^ |
           
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          Maybe there's something wrong in your code , here's one of AC solutions code

          as you can see it did nothing more than DFS with memorization to states

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          12 years ago, hide # ^ |
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          We have 5 x 6 board. Each column can be some subset of itself, but some subsets are unreachable. It gives higher bound to 2^30 states. Note it's a higher bound and in practice is not reachable.

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            12 years ago, hide # ^ |
             
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            I also suspect this with my backtracking aprouch without prunning

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      12 years ago, hide # ^ |
       
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      Simple prunning that helps a lot — you definitely can't solve a board where you have only one object of some type left.

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