I've created a mashup contest on Codeforces.

But it seems that the contest's registration opens the same day.

Is there any way such that the registration begin time earlier so that I could share participants with the contest's url and let them register the contest themselves?

Given a & b(where(1<=a,b<=20), find sum of all integers whose digit sum is exactly $$$a^{b}$$$.

Return sum%10^9+7

Update: Sorry I missed one thing. The sum of all numbers whose each digit is non-zero.

Thank you very much for going live again.

First of all I am really excited about it. Who doesn't want to participate in contests !!! Secondly, there are some things that can be accounted for.

Some acknowledgements(we all know) :

1.Rating and divisions
    Div1-->[1900,9999)
    Div2-->[0,2100)
    Div3-->[0,1600)
    Div4-->[0,1400)

2.There a 4 types of contests held here. 
    a) Type #1: DIV1+DIV2 -->Rating range[0,9999)
    b) Type #2: DIV1-->[1900,9999) & DIV2-->[0,1900) separately on the same round
    c) Type #3: DIV2-->[0,2100)
    d) Type #4: DIV3-->[0,1600)

Now as MikeMirzayanov said, "the number of gray and green participants in total exceeds the number of other participants.". I think slightly modified type of contest may be added.

a) Type #1: DIV1+DIV2+DIV3-->Rating range[0,9999)
b) Type #2: DIV1-->[1900,9999) & DIV2-->[1400,1900) & DIV3-->[0,1400) separately on the same round
c) Type #3: DIV2+DIV3-->[0,2100)
d) Type #4: DIV2-->[1400,2100) & DIV3-->[0,1400) separately on the same round
e) Type #5: DIV3-->[0,1600)

I think this might work.

Can anyone please verify my implementation of Iterative Merge Sort ? I need to know that is it correct and can I use it in solving problems. The code is commented as my level. Thanks in advance.