Try dp states can be position of digit, prev digit, greater than next, state to maintain if number has gone greater than a, state to maintain number has gone less than b

For greater than a and less than b we start setting msb first so if most significant digit is greater than a set greater than a to be one else the digit has to be same as a No such restriction applies once greater than a is set Similarly we can proceed for less than b

Why negative upvotes, i was just unable to solve question during contest so asking for help??

Or if you need an editorial ;P https://discuss.codechef.com/questions/4270/sumslope-editorial which was published 4 years before time :