The technique of converting is a major trick in counting.
convert to the problem you can solve, and use combinatory
所有跟帖:
• 2^(n-1)*n!/((2n)!/2^n) -mondayadvisor- ♀ (809 bytes) () 10/22/2015 postreply 19:58:01
The technique of converting is a major trick in counting.
• 2^(n-1)*n!/((2n)!/2^n) -mondayadvisor- ♀ (809 bytes) () 10/22/2015 postreply 19:58:01