factorial

C#: Recursive functions with Lambdas

由 不羁岁月 提交于 2019-11-26 17:38:33
问题 The below does not compile: Func<int, int> fac = n => (n <= 1) ? 1 : n * fac(n - 1); Local variable 'fac' might not be initialized before accessing How can you make a recursive function with lambdas? [Update] Here are also two links that I found interesting to read: Eric Lippert's "Why does a recursive lambda cause a definite assignment error?" Anonymous Recursion in C# 回答1: This particular style of function is not supported by C# as a single line declaration. You have to separate out the

StackOverflowError computing factorial of a BigInteger?

由 丶灬走出姿态 提交于 2019-11-26 16:59:51
问题 I am trying to write a Java program to calculate factorial of a large number. It seems BigInteger is not able to hold such a large number. The below is the (straightforward) code I wrote. public static BigInteger getFactorial(BigInteger num) { if (num.intValue() == 0) return BigInteger.valueOf(1); if (num.intValue() == 1) return BigInteger.valueOf(1); return num.multiply(getFactorial(num.subtract(BigInteger.valueOf(1)))); } The maximum number the above program handles in 5022, after that the

Cannot calculate factorials bigger than 20! ! How to do so?

由 做~自己de王妃 提交于 2019-11-26 16:35:45
问题 I am using unsigned long long integer format in order to calculate big factorials. However my code fails at some point can you have a look at it? Actually it is part of a larger code for Taylor expansion of exponential function, but that part is irrelevant at this point. I will appreciate any suggestions. Thanks #include <stdio.h> #include <math.h> //We need to write a factorial function beforehand, since we //have factorial in the denominators. //Remembering that factorials are defined for

Memoized, recursive factorial function?

由 ￡可爱￡侵袭症＋ 提交于 2019-11-26 16:21:46
问题 I know how to do memoization in Python easily but I need a faster way to compute them, so I am using C++. However, I have no clue how to memoize. I understand that it's about storing values into an array or vector and then scanning for its value when retrieving, but it'd be really helpful to see how this is done so I can try its speed. 回答1: Well the neatest way I can think of to do this in C++ is probably using a function object to store the memoized values. I guess this is probably slightly

Example of O(n!)?

由 |▌冷眼眸甩不掉的悲伤 提交于 2019-11-26 15:34:00
问题 What is an example (in code) of a O(n!) function? It should take appropriate number of operations to run in reference to n ; that is, I'm asking about time complexity. 回答1: There you go. This is probably the most trivial example of a function that runs in O(n!) time (where n is the argument to the function): void nFacRuntimeFunc(int n) { for(int i=0; i<n; i++) { nFacRuntimeFunc(n-1); } } 回答2: One classic example is the traveling salesman problem through brute-force search. If there are N

Fast way to calculate n! mod m where m is prime?

由 ￡可爱￡侵袭症＋ 提交于 2019-11-26 14:26:54
I was curious if there was a good way to do this. My current code is something like: def factorialMod(n, modulus): ans=1 for i in range(1,n+1): ans = ans * i % modulus return ans % modulus But it seems quite slow! I also can't calculate n! and then apply the prime modulus because sometimes n is so large that n! is just not feasible to calculate explicitly. I also came across http://en.wikipedia.org/wiki/Stirling%27s_approximation and wonder if this can be used at all here in some way? Or, how might I create a recursive, memoized function in C++? Expanding my comment to an answer: Yes, there

What is the fastest factorial function in JavaScript?

由 笑着哭i 提交于 2019-11-26 12:42:27
Looking for a really fast implementation of factorial function in JavaScript. Any suggests? Margus You can search for (1...100)! on WolframAlpha to pre-calculate the factorial sequence. The first 100 numbers are: 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600, 6227020800, 87178291200, 1307674368000, 20922789888000, 355687428096000, 6402373705728000, 121645100408832000, 2432902008176640000, 51090942171709440000, 1124000727777607680000, 25852016738884976640000, 620448401733239439360000, 15511210043330985984000000, 403291461126605635584000000,

Calculate the factorial of an arbitrarily large number, showing all the digits

由 橙三吉。 提交于 2019-11-26 12:16:54
I was recently asked, in an interview, to describe a method to calculate the factorial of any arbitrarily large number; a method in which we obtain all the digits of the answer. I searched various places and asked in a few forums. But I would like to know if there is any way to accomplish this without using libraries like GMP. Thank you. GNU Multiprecision library is a good one! But since you say using of external libraries are not allowed, only way I believe its possible is by taking an array of int and then multiplying numbers as you do with pen on paper! Here is the code I wrote some time

OverflowError: long int too large to convert to float in python

由 邮差的信 提交于 2019-11-26 11:28:44
问题 I tried to calculate poisson distribution in python as below: p = math.pow(3,idx) depart = math.exp(-3) * p depart = depart / math.factorial(idx) idx ranges from 0 But I got OverflowError: long int too large to convert to float I tried to convert depart to float but no results. 回答1: Factorials get large real fast : >>> math.factorial(170)

Fast exact bigint factorial

由 ﹥＞﹥吖頭↗ 提交于 2019-11-26 03:59:30
问题 I have a fixed-point bignumber library and want to implement fast factorial with no precision loss. After some math tricks on paper I got this formula: (4N)!=((2N)!).((2N)!).{ (2N+1).(2N+3).(2N+5)...(4N-1) }.(2^N)/(N!) This is already pretty fast, and with some programming tricks the complexity nears ~ O(log(n)) . To be clear, my current implementation is this: //--------------------------------------------------------------------------- longnum fact(const DWORD &x,longnum &h) // h return (x>
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