factorial

For class I have an assignment: Write a C++ program that will output the number of distinct ways in which you can pick k objects out of a set of n objects (both n and k should be positive integers). This number is given by the following formula: C(n, k) = n!/(k! * (n - k)!) Your program should use two value-returning functions. The first one should be called factorial and should return n! . The second function should be called combinations and should return n!/(k! * (n - k)!). Test your program for different values of n and k five times (count-controlled loop). I came up with a solution:

I have a list of N items and I am wondering how I can loop through the list to get every combination. There are no doubles, so I need to get all N! orderings. Extra memory is no problem, I'm trying to think of the simplest algorithm but I'm having trouble. See std::next_permutation Expanding on others' answers, here's an example of std::next_permutation adapted from cplusplus.com #include <iostream> #include <algorithm> using namespace std; void outputArray(int* array, int size) { for (int i = 0; i < size; ++i) { cout << array[i] << " "; } } int main () { int myints[] = { 1, 2, 3, 4, 5 };

As a part of my BigDecimal library, I need to calculate the factorial of any given non negative integer. So I'm using .Net 4.0 's System.Numerics.BigInteger to be able to store huge numbers. Here is the function I'm using: private BigInteger Factorial(BigInteger x) { BigInteger res = x; x--; while (x > 1) { res *= x; x--; } return res; } It's working but not optimized. Now I want to use parallel computing, so here is what I've tried: (I have no experience with parallel programming) public BigInteger Factorial(long x) { BigInteger res = 1; ParallelLoopResult r = Parallel.For(2L, (x + 1), i =>

I want to calculate the sum of digits of N!. I want to do this for really large values of N, say N(1500). I am not using .NET 4.0. I cannot use the BigInteger class to solve this. Can this be solved by some other algorithm or procedure? Please help. I want to do some thing like this Calculate the factorial of an arbitrarily large number, showing all the digits but in C#. However I am unable to solve. There is no special magic that allows you to calculate the sum of the digits, as far as I am concerned. It shouldn't be that hard to create your own BigInteger class anyway - you only need to

I coded 3 factorial algorithms: First, I expect to fail by Stack Overflow. No problem. Second, I try tail recusive call , convert previous algorithm from recursive to iterative. It doesn't work but I don't understand why . Third, I use trampoline() method and works fine as I expect. def factorial factorial = { BigInteger n -> if (n == 1) return 1 n * factorial(n - 1) } factorial(1000) // Stack Overflow factorial = { Integer n, BigInteger acc = 1 -> if (n == 1) return acc factorial(n - 1, n * acc) } factorial(1000) // Stack Overflow, why??? factorial = { Integer n, BigInteger acc = 1 -> if (n =

How can I make a function that calculates the factorial (or the gamma function ) of decimal numbers in JavaScript? For example, how could I calculate 2.33! ? I might have found an existing solution... It's an implementation of Lanczos method, I found it at the swedish wikipedia ( http://sv.wikipedia.org/wiki/Gammafunktionen ). It was written in python and says to be correct up to 15 decimals. I ported it to js, cross checked some random values against ( http://www.efunda.com/math/gamma/findgamma.cfm ). http://jsfiddle.net/Fzy9C/ var g = 7; var C = [0.99999999999980993, 676.5203681218851, -1259

I've compaired the scala version (BigInt(1) to BigInt(50000)).reduce(_ * _) to the python version reduce(lambda x,y: x*y, range(1,50000)) and it turns out, that the scala version took about 10 times longer than the python version. I'm guessing, a big difference is that python can use its native long type instead of creating new BigInt-objects for each number. But is there a workaround in scala? Travis Brown The fact that your Scala code creates 50,000 BigInt objects is unlikely to be making much of a difference here. A bigger issue is the multiplication algorithm— Python's long uses Karatsuba