回复：没关系，说一下大概思路，这种counting题，常会出错

I wish i can type chinese, but i'm at work...

here's my idea, not sure if it's correct strategy though.... there're 3 situations:

1. none of the 4 repeating ones fall in 1st position(million-th) & not zero (15*9*8*8*7)

2. the 4 repeating one start on 1st position  (20*9*9*8*7)

3. the 4 repeating ones are zeros (15*1*9*8*7)

add the 3 up, then it goes my answer. hopefully you get the correct answer and let me know if i'm right :).

what grade is this question for?