a<b<c<d<e<f<g<h<i
- - - - - - - -
(each symbol represents a "less than or equal to" )
For example, 123456789 or 122223455
How many 9-digit number would satisfy the given condition ?
更新1:
it is a is less than or equal to b is less than or equal to c is less than or equal to d is less than or equal to e is less than or equal to f is less than or equal to g is less than or equal to h is less than or equal to i
