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hi all, i try this question because i really love the song :lol:
however i cannot solve the problem (WA) :cry:

could anyone help and give me some critical test data? thanks a lot
i don't post my problem as i simply use the hints from the old posts (hope i understand the hint correctly)

here are ...

Sorry for late solaris :(
thanks for your advice.
But i am facing some problems>>>>
firstly, i am afraid about the time complexity in using backtracking.
2nd ly implementating backtracking is seems to be hard to me..
i think to find the case of "impossible" & "unique" the total tree will be ...