第4个回答 2010-03-24
Mathematica 代码:
arr = Table[j, {j, 1, 5}];
brr = Permutations[arr];
crr = Reverse[Cases[brr, x_ -> FromDigits[x]]]
Length@crr
crr[[95]]
结果:
{54321, 54312, 54231, 54213, 54132, 54123, 53421, 53412, 53241,53214, 53142, 53124, 52431, 52413, 52341, 52314, 52143, 52134, 51432, 51423, 51342, 51324, 51243, 51234, 45321, 45312, 45231, 45213, 45132, 45123, 43521, 43512, 43251, 43215, 43152, 43125, 42531, 42513, 42351, 42315, 42153, 42135, 41532, 41523, 41352, 41325, 41253, 41235, 35421, 35412, 35241, 35214, 35142, 35124, 34521, 34512, 34251, 34215, 34152, 34125, 32541, 32514, 32451, 32415, 32154, 32145, 31542, 31524, 31452, 31425, 31254, 31245, 25431, 25413, 25341, 25314, 25143, 25134, 24531, 24513, 24351, 24315, 24153, 24135, 23541, 23514, 23451, 23415, 23154, 23145, 21543, 21534, 21453, 21435, 21354, 21345, 15432, 15423, 15342, 15324, 15243, 15234, 14532, 14523, 14352, 14325, 14253, 14235, 13542, 13524, 13452, 13425, 13254, 13245, 12543, 12534, 12453, 12435, 12354, 12345}
120
21354