回复：c Could you provide some details for

3) for any n in C, f(n) <= 2c (why?)

6) for each b in B, there is an unique a in A, with f(a)=b (why?)

And from 6), one can only say number of elements in B <= number of element in A.

 

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• figure out missing details. Nice problem and nice solution. -wxcfan123- ♂ (335 bytes) () 06/12/2011 postreply 14:36:53