Problem Strange Function from December Lunchtime 2017 matches exactly with problem I: Repeated Digit Sum from ACM-ICPC Dhaka Site Preliminary Contest 2017 !!
Codechef Lunchtime was held on 30 December 2017.
ACM-ICPC Asia Dhaka Site Preliminary Contest was held on 23 September 2017.
Author of the problem on codechef was: abx_2109, tester: kingofnumbers
Author of the problem for ICPC Dhaka Site Preliminary was: Jane Alam Jan [Founder of LightOJ, alternate writter was: Hasnain Heickal Jami
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Also, the problem set was officially uploaded to the website of hosting university, and the link to that was also added in ACM_ICPC Baylor website.
In this link icpc page see at the right side, under check out, the problem link is given, which is: problems
Hello!
The function that is asked in my problem i.e F(X) is quite an old and a popular function and is available on many websites(including wikipedia).Its called digital root. Just have a look here. From this blog 5th point I first read about this function that takes the repeated sum of the digits of a number.Here only the property F(X*X)=F(F(X)*F(X))(commonly called multiplication property of digital roots) is mentioned which I have used for my problem.This blog is way older than Dhaka regional contest september,2017.So I haven’t copied from anywhere. I hope this clears your doubt.
This is a very popular function and has been used a lot of times before as well(even i have solved qns of this type before). A very false accusation according to me.