000 -
001
002
010 -
011
012
020 -
021
022
100 -
101
102
110 -
111
112
120 -
121
122
200 -
201
202
210-
211
212
220-
221
222


000
001
010
011
100
101
110
111




move left to right up to the first not max-value digit, 
increase it, 
if it is now max-value 
then reset all previous digits to the lowest value.