numbers

I'd like to write a program that lets users draw points, lines, and circles as though with a straightedge and compass. Then I want to be able to answer the question, "are these three points collinear?" To answer correctly, I need to avoid rounding error when calculating the points. Is this possible? How can I represent the points in memory? (I looked into some unusual numeric libraries, but I didn't find anything that claimed to offer both exact arithmetic and exact comparisons that are guaranteed to terminate.) Yes. I highly recommend Introduction to constructions , which is a good basic

I'm developing an online form in which user-entered Medicare numbers will need to be validated. (My specific problem concerns Australian Medicare numbers, but I'm happy for answers regarding American ones too. This question is about Medicare numbers in general.) So how should I do it? (It would be good to have the answer in Javascript or a regex.) The regex supplied by Jeffrey Kemp (March 11) would help to validate the allowed characters, but the check algorithm below should be enough to validate that the number conforms to Medicare's rules. The Medicare card number comprises: Eight digits; A

I am using this code to generate a 8 digit unique number. byte[] buffer = Guid.NewGuid().ToByteArray(); return BitConverter.ToUInt32(buffer, 8).ToString(); Does this code really generate a unique number or might it repeat the same number again? Marnix van Valen A GUID is not just a random number; it's composed of segments. Some of the segments will not change at all if the guid is generated on the same computer. By using only 64-bits of the original 128-bits you are breaking the structure of the guid and most likely breaking the uniqueness of the generated number. This question has more info

I am trying to create a program that will tell if a number given to it is a " Happy Number " or not. Finding a happy number requires each digit in the number to be squared, and the result of each digit's square to be added together. In Python, you could use something like this: SQUARE[d] for d in str(n) But I can't find how to iterate through each digit in a number in Java. As you can tell, I am new to it, and can't find an answer in the Java docs. You can use a modulo 10 operation to get the rightmost number and then divide the number by 10 to get the next number. long addSquaresOfDigits(int

What's the most efficient algorithm anyone can think of that, given a natural number n , returns the least natural number x with n positive divisors (including 1 and x )? For example, given 4 the algorithm should result in 6 (divisors: 1,2,3,6); i.e. 6 is the smallest number having 4 distinct factors. Similarly, given 6, the algorithm should result in 12 (divisors: 1,2,3,4,6,12); i.e. 12 is the smallest number having 6 distinct factors In terms of real-world performance, I'm looking for a scalable algorithm which can give answers of the order of 10 20 within 2 seconds on a machine which can do

How do I quickly generate a random prime number, that is for sure 1024 bit long? Generate 1024 random bits. Use a random source that is strong enough for your intended purpose. Set the highest and lowest bits to 1. This makes sure there are no leading zeros (the prime candidate is big enough) and it is not an even number (definitely not prime). Test for primality . If it's not a prime, go back to 1. Alternatively, use a library function that generates primes for you. Use a library function, such as OpenSSL. There's no need to write this yourself. Example: http://ardoino.com/7-maths-openssl