This is a problem from 2021 ICPC Shannxi invitational and confuse me a lot. Since this contest have neither place to up-solving nor tutorial, I'm here to ask for idea and help.↵
↵
The problem is like:↵
↵
Given a number X, we call another number N is a lucky number to X if:↵
↵
1. N is larger than 1e8;↵
2. N is smaller than 1e13;↵
3. (N!) begins with X.↵
↵
For example, if we ignore the first constraint, N=10 is a lucky number to X=3628 since (10!)=3628800.↵
↵
Now, given T testcases, each testcases gives you a X, output any N where N is a lucky number to X.↵
↵
T is smaller than 200 and X is smaller than 1e5.↵
↵
Sample input↵
↵
2↵
↵
494↵
↵
997↵
↵
Sample output↵
↵
1000001586369↵
↵
1000001980150↵
↵
UPD: Thanks everybody for helping, I think using stirling's and brute force is the right one.
↵
The problem is like:↵
↵
Given a number X, we call another number N is a lucky number to X if:↵
↵
1. N is larger than 1e8;↵
2. N is smaller than 1e13;↵
3. (N!) begins with X.↵
↵
For example, if we ignore the first constraint, N=10 is a lucky number to X=3628 since (10!)=3628800.↵
↵
Now, given T testcases, each testcases gives you a X, output any N where N is a lucky number to X.↵
↵
T is smaller than 200 and X is smaller than 1e5.↵
↵
Sample input↵
↵
2↵
↵
494↵
↵
997↵
↵
Sample output↵
↵
1000001586369↵
↵
1000001980150↵
↵
UPD: Thanks everybody for helping, I think using stirling's and brute force is the right one.
