In the above problem, we have 3 numbers, a,b and c, and we’ve to find a^b%c. Here’s the code I’ve written:
#include
using namespace std;
int main() {
int a,b,c;
cin>>a>>b>>c;
int power=1,ans;
for(int i=1;i<=b;i++)
{
power*=a;
}
ans=power%c;
cout<<ans;
return 0;
}
Why are 6 of the 10 test cases failing?
Modular exponentiation issue
Hello @Rohanaggarwal8590,
I apologize for replying late.
I somehow forgot to answer your doubt. I hope, you’ll understand.
The failure of code is due to the following reason:
The maximum value a and b can have is 100000.
What you are are doing is a^b i.e. 100000^100000.
Is there any datatype available to store this big(infinitely big) value?
No, is the answer.
This, is the reason you are getting wrong output. If you want to verify this, then I would suggest you to print ans and see what it print.
Think of a different way to calculate modular exponential.
Hint: study about exp. by squaring method algorithm.
Refer the below mentioned link for details:
https://www.google.com/url?sa=i&source=web&cd=&ved=2ahUKEwiW37bntJTjAhXXWisKHU6SAswQzPwBegQIARAC&url=https%3A%2F%2Fwww.geeksforgeeks.org%2Fexponential-squaring-fast-modulo-multiplication%2F&psig=AOvVaw1vw3oDqn1bMtovjRL8iMdC&ust=1562094281766744
If you still have doubts, feel free to ask.
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