an enumerating the answer week

ARC079 took place on Saturday night as usual. I stuck on problem E, and as a result, missed the chance to get into the first page of the standings. Problem E was a tricky problem. Here's a hint. When the maximum number is less than \(n\), the sum of all numbers will not be greater than \(n\).

Then CF#426 took place one day later. After messing up problem A, I skipped problem B and C and managed to solve D, and finally ranked 8 thanks to this strategy and became an igm! Problem B and D were basic data-structure problems and there's nothing to talk about it. Problem C was very tricky. Here's what the problem looks like. Define \(f(x) = y\), where \(y\) is the number which obtained by sorting all digits of \(x\) in non-decreasing order. One need to calculate how many different \(f(x)\) values there are where \(L \leq x \leq R\). \((1 \leq L \leq R \leq 10^{18})\) Do you guys know how to solve it?