Infinite Adder
Write a program that can add 2 integers of ANY LENGTH (limited only by computer memory). Store the 2 integers as a linked list of digits (each node is a single digit from 0 – 9). Read each number from a comma-delimited file of digits in reverse order (for example, a file with “2,3,7,0,1” represents the number 10732). One file should be called “num1.txt” and the other file should be called “num2.txt”. The Hard Part: When you print out the answer, it should be in “normal” order.
It may be wise to write a doubly-linked list in order to make things easier.
Help would be very much appreciated.
I can tell you what I need to do, but I don't know how to write it code-wise.
Related
I am generating random OTP-style strings that serve as a short-term identifier to link two otherwise unrelated systems (which have authentication at each end). These need to be read and re-entered by users, so in order to reduce the error rate and reduce the opportunities for forgery, I'd like to make one of the digits a check digit. At present my random string conforms to the pattern (removing I and O to avoid confusion):
^[ABCDEFGHJKLMNPQRSTUVWXYZ][0-9]{4}$
I want to append one extra decimal digit for the check. So far I've implemented this as a BLAKE2 hash (from libsodium) that's converted to decimal and truncated to 1 char. This gives only 10 possibilities for the check digit, which isn't much. My primary objective is to detect single character errors in the input.
This approach kind of works, but it seems that one digit is not enough to detect single char errors, and undetected errors are quite easy to find, for example K37705 and K36705 are both considered valid.
I do not have a time value baked into this OTP; instead it's purely random and I'm relying on keeping a record of the OTPs that have been generated recently for each user, which are deleted periodically, and I'm reducing opportunities for brute-forcing by rate and attempt-count limiting.
I'm guessing that BLAKE2 isn't a good choice here, but given there are only 10 possibilities for the result, I don't know that others will be better. What would be a better algorithm/approach to use?
Frame challenge
Why do you need a check digit?
It doesn't improve security, and a five digits is trivial for most humans to get correct. Check if server side and return an error message if it's wrong.
Normal TOTP tokens are commonly 6 digits, and actors such as google has determined that people in general manage to get them orrect.
I need to know how to create a list of number in 8085 assembler and store the list in successive memory location?
Most assemblers will have a set of define statements and a way to specify different bases.
For example, the values zero, one and forty-two, along with a short nul-terminated string, may be created with something like:
some_vals: db 0, 1, 2Ah, 'hello', 0
How your assembler does it is probably in the documentation somewhere. Without more specific details on which assembler you're using, this not much more help I can give.
Pseudo-ops like data definition (db, dw, ds), address specification (org) or label setting (mylabel:) do not generally form part of the processor documentation itself, rather they're a function of the assembler.
See, for example, chapter 4 of this document. I particularly love the fact that we used to buy these 200-page books for $3.95 whereas now you'll be shelling out a hundred bucks for a digital copy with no incremental cost of production :-)
I'm working on a project where I need to send a value between two pieces of hardware using CoDeSys. The comms system in use is CAN and is only capable of transmitting in Bytes, making the maximum value 255.
I need to send a value higher than 255, I'm capable of splitting this over more than one byte and reconstructing it on the receiving machine to get the original value.
I'm thinking I can divide the REAL value by 255 and if the result is over 1 then deconstruct the value in to one byte holding the remainders and one byte holding the amount of 255's in the whole number.
For example 355 would amount to one byte of 100 and another of 1.
Whilst I can describe this, I'm having a really hard time figuring out how to actually write this in logic.
Can anyone help here?
This is all handled for you in CoDeSys if I understand you correctly.
1. CAN - Yes it's in byte but you must not be using CANopen you are using the low level FB that ask you to send a CAN frame of an 8 byte array?
If it is your own two custom controllers ( you are programming both of them in CoDeSys) just use netvariables. Netvariables allows you to transfer any type of variable and you can take the variable list from one controller and import it to another controller and all the data will show up. You don't have to do any variable manipulation it's handle under the hood for you. But I don't know the specifics of your system and what you are trying to do.
If you are trying to deconstruct construct variables from one size to another that is easy and I can share that code with you.
I have streaming strings (text containing words and number).
Taking one line at a time for streaming strings, I would like to assign a unique value to them.
the examples may be:strings with their scores/hash
User1 logged in Comp1 port8087 1109
User2 logged in comp2 1135
user3 logged in port8080 1098
user1 logged in comp2 port8080 1178
these string should be in same cluster. For this what i have thought is mapping(bad type of hashing) the strings such that the small change in the string wont affect the score that much.
One simple way of doing that may be: taking UliCp8, Ulic .... ( i.e. 1st letter of each sentence) and find some way of scoring. After then the similar scored strings are kept in same bucket and later on sub group them.
The improved method would be: lets not take out first word of each word of the string but find some way to take representative value of the word such that the string representation may be quite suitable for mapping with score/hash as i mention.
Considering Levenstein distance or jaccard_index or some similarity distance metrices, all of them require inputting the strings for comparisions. Isn't there any method to hash/score the string as stated without going for comparisions.( POS tagging, comparing looks uneffiecient for my purpose as the data are streaming, huge in number, unstructured)
Hope you understand what i want to achieve and please help me out. Forgot about the comments below and lets restart.
"at least two similar word (not considering length) should have similar hash value"
This is against the most basic requirements for a hash function. With a hash function also minimal changes to the input should produce vehement changes to the bucket the hash falls into.
You are looking for an algorithm that calculates the similarity or distance between two inputs.
As stated you are not looking for a hash function, rather something like the Levenshtein distance which is an algorithm for calculating a metric representing the degree of differences between two sequences of bits. It is commonly used to find out how similar/dissimilar two strings are. Hashing / message digests are good for creating identifiers for unique, distinct values but they will produce entirely different results for "similar" values.
You are interested in the similarity of strings. Here is a nice post that names a few resources that are used for measuring string similarity. Maybe Lucene could help you in your situation.
We would like to give each of users an alias so that we can refer to them in discussions while protecting their identity. These aliases should be unique.
The easy way would be to simply use a SERIAL column, but ints aren't memorable. We would like to use real people names so that we can remember the aliases.
The other easy way would be to find a list of first names somewhere, number them, and use a SERIAL to fetch names from the list. When the list runs out, add more names.
But is there some clever way to map ints to names?
We currently have about 2,000 users and are growing, but I doubt we'll ever become Google.
It may sound crazy. But there is an algorithm used in game programming to create meaningless but phonetically unique names like Alveolar, Bilabial, Glottal, Palatal, Velar.
Pick a random name from the Census Bureau's names file.
Have you tried any Hash functions? I am not sure whether they are available in Postgres. But yeah, one way to do is let the internal hash function take care. They will output unique IDs.
Back in "the day" Compuserve (or was it AOL?) used to give out temporary, initial passwords by having two lists of words and taking one word from each list and putting it together, so you would get something like EasyTomato or whatever. Perhaps something like that would work for your user base. If each word list has 256 characters, that's 65535 unique combinations (and notice how easily you can pick the combination by just incrementing a 16-bit integer).
EDIT: Well don't do a straight increment of the integer after all, or the first 256 people will all get the same first word, but the basic idea is still sound. Pick a random, not-yet-used 16-bit number. High 8 bits are your index into the first word list, low 8 bits are your index into the second word list.