1到10组成4位数,就是1到九组成四位数,不重复的4位数最终有5040个,算法是6乘以7乘以8乘以9乘以10等于5040,比如就有有1234,2345,3456,6789,1023,1024,1025,1026,1027,1028,1029,1032,1034,1035,1036,1037,1038,1039,1042,1043,1045,1046,1047,1048等等