This question already has an answer here:
What variable type for extremely big integer numbers?
(1 answer)
Closed 7 years ago.
How can i implement "Big-Integer" for c/c++ programming? Is there any build function in c/c++ library? or do I have to implement the Function for it?
{
BigInt fac=1;
int value=25;
for(int i=1;i<=25;i++){
fac=fac*i;
}
cout<<fac<<endl;
}
I am trying like this but seems like there is no data type like "Big Int" .
You can use boost::multiprecision::cpp_int if you need an arbitrary precision integer. If you need it to be fast, you can use boost::multiprecision with linking to one of several options of an external back-end.
Using a array to store the single integers at a time will help you achieving the desired effect!
This is the one of the best tutorial from codechef for this well known big-int problems!
Hope that helps!
Related
This question already has an answer here:
What variable type for extremely big integer numbers?
(1 answer)
Closed 6 years ago.
"unsigned long int" keeps becoming 0. It has to be a really big integer that I can operate multiplication and modulo on.
Example: 1234^123 % 1234
If you're using gcc you can try __uint128_t or maybe use double instead unless you need to do bitwise operations
Two roads you got
1. Implement what you need by learning how to do large calculations using integer arrays with maths tricks for speed up OR
2. Use a library
I would suggest to go with 2nd option if you are not tied to use external library. One such bigNum library is ttmath
OR
If you have a option to switch to java, then java has builtin BigInteger, BigDecimal and more functionalities supported. Look at BigInteger javadoc
This question already has an answer here:
Which is a good C++ BigInteger class for programming contests?
(1 answer)
Closed 7 years ago.
I would like to know how to use very large numbers (being accurate 10^100 in C++) for competitive programming. I know libraries like GMP exist but they can't be used sites like SPOJ or CodeChef.
I have used strings, however it takes lot of time to implement it. Now I would like to know what efficient methods do other programmers use and resources to learn those methods. Thanks!
I would like to know what efficient methods other programmers use
Most of the time you can't use any third-party libraries when submitting your solutions to online judge systems like SPOJ or at contests (however some contests need only .out files, so it doesn't matter how you get them).
Since you cannot use anything external, competitive programmers write their BigNum classes on their own. It is not really so hard using dynamic arrays or data structures like std::string in C++.
How to?
Practice is your best friend when you are trying to beat and solve online judge/contest problems.
Paper, pencil, your mind, nothing else is required to find out how to implement your BigNum class.
Consider how you can read/write big numbers as std::string, then go one level further and try to add/remove leading-zeros, count a sum of two big numbers... and then, further things will be easier.
This question already has answers here:
How to convert Byte Array to Hexadecimal String in C++?
(4 answers)
Closed 9 years ago.
There are a lot of different ways to convert a byte array to a hex string. What is the fastest way?
C-style sprintf
C-style lookups
C++-style stringstream
There are possibly more.
Testing over 100,000 iterations found:
the lookups solution took 63 ms.
the sprintf solution took 827 ms (~10x more than #1).
the stringstream solution took 1684 ms (~25x more than #1).
All results from my own test system.
This is probably a surprise to no one very familiar with C and C++ but given the number of different approaches available for solving this problem, having a Q&A on the approach with the best performance could be useful for people less familiar with C/C++.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Using arrays or std::vectors in C++, what's the performance gap?
I just wanna know which of them are the faster and use less resources? I think that vector is more reliable and secure but a pointer to an array is faster. I want to re-size the array (add new elements, so increment it by 1 or remove elements from it). A vector has its functions for that while a pointer needs one created by me.
I don't know which one to choose. What do you advise me? Thanks!
According to Bjarne Stroustrup, you should use vector over Array unless you have a really good reason to use an array.
The c++ standard libaries have been optimized to be as fast as possible all the while providing necessary functions so that you do not have to implement them. Save yourself the time and worry and just use a vector.
If there are any discrepancies on speed they will be negiligble in the big picture :)
This question already has answers here:
Closed 14 years ago.
How can I add very large numbers in C++?
consider a "bignum" library like: http://gmplib.org/ or http://ttmath.slimaczek.pl/ttmath. take a look at a simple bignum class: http://www.circlemud.org/~jelson/560/
Do a Google on "Bigint C++" This will provide you with a list of arbitrator precision integer arithmetic libraries.
You can find a big decimal implementation at http://speleotrove.com/decimal/
How big is "very large"? A signed long int can go up to 2,147,483,647 and an unsigned long int can go up to 4,294,967,295.
GMP has a GMPXX C++ wrapper which is kind of nice. GMP supports both integer and floating point numbers, and is LGPL'ed.
I've used it. It's ok, but watch out for creating lots of temporaries. (Potential efficiency hit.)
You could use a library like LiDIA for a 'big integer' class.