i have to generate all possible Combination of a Name 'Tony Stark'.
Like noty, onty etc.
and after generating all possible Names Combination ,
We have to create Accounts for All Names Combination.
Thank You.
Let me know that, if you get my solution in comment
You need to generate all possible combination on given String (or say Name) which means all rearrangement of the name letter of an ordered into a one-to-one correspondence.
A string of length n has n! permutation.
So I suggest you can go with two method:-
Backtracking Algorithim with Time Complexity: O(n*n!)
Or you can use substring method of Apex String with for Loop to get all the combination Time Complexity: O(n*n!)
Let me know if you have any other query on this, if you have written the code then you can also post here and I can look into that.
Thanks.
Related
I am trying to take a text string and create a unique numerical value from it and I am not having any luck.
For example, I have user names (first and last) and birthdate. I have tried taking these values and converting them to varbinary, which does give me a numerical value from the data, but it isn't unique. Out of ~700 records, I will get at least 100 numerical values that are duplicated but the text of first name, last name, and birthdate that was used to generate the number is different.
Here is some code I have been trying:
SELECT CONVERT(VARCHAR(300), CONVERT(BIGINT,(CONVERT(VARBINARY, SE.FirstName) + CONVERT(VARBINARY, SE.BirthDate) ))) FROM ELIGIBILITY SE
If I use that code and convert the following data, the result is 3530884780910457344. So the same number is generated from this unique data:
David 12/03/1952
Janice 12/23/1952
Michael 03/24/1952
Mark 12/23/1952
I am looking for some way, the simpler the better, to take these values and generate a unique numerical value from that data. And the reason why I need to use these values as input is because I am trying to avoid creating duplicates in the future as well as be able to predict the numerical value based on the formula. This is why NewID() won't work for me.
How about simply:
SELECT CHECKSUM(name, BirthDate) FROM dbo.ELIGIBILITY;
Of course, since there are still chances for collisions, maybe you should better define what you are actually trying to do. You've stated some reasons why e.g. NEWID() won't work but I still don't follow the the underlying purpose of this unique number.
i am in search for a good Hash function which i can use in Hash table implementation. The thing is that i want to give both strings and integers as parameters(keys) in my hash function.
i have a txt file with ~500 data and every one of them consists of integers and strings(max 15 chars). So, the thing that i want to do is to pick one of these ints/strings and use it as a key for my hash function in order to put my data in the "right" bucket.
Is there any good function to do this?
Thank you :)
Use the Integer value if that's present & reasonably well distributed, then hash the String if it's not. Integer hashcode is much cheaper to compute than String.
The algorithm has to be repeatable, obviously.
Your question is somewhat vague. It's unclear if your data set has 500 columns and you are trying to figure out which column to use for hashing, or if it has 500 items which you want to hash.
If you are looking for a decent general purpose hash that will produce well-distributed hash values, you may want to check out the Jenkins hash functions which have variants for strings and integers. But, to be frank, if your dataset has 500 fixed items you may want to look at a perfect hash function generator, like GNU gperf or even alternative data structures depending on your data.
Since you want to hash using two keys, I presume the distribution improves using two keys.
For string hashing, I have had good results with PJW algorithm. Just google for "PJW Hash String". One variation here
To augment the hash with an integer, see here
I am working in C. To store a set of words for searching through them, I am told to save them in a hash table, and that it will reduce the time complexity to a constant.
Can someone help me out with the hash function? Also, if I have around 25 keywords, can I just make a table of size 25 and map each keyword to an index?
One option is to look for a perfect hash function, a hash function for which collisions don't exist. The Linux tool gperf (not gprof) can be used to automatically generate a perfect hash function from a set of strings. As others have pointed out this is unlikely to give you a huge performance boost unless lookup times are a large part of your program, but it should speed up the lookups.
Hope this helps!
At just 25 entries, a hash table won't bring you much benefit. Just do a linear search instead.
At just 25 strings to match, hashing won't add up to the efficiency. You could look into Horspool Algorithm for string matching, that should work well! And as Bo mentioned you could store them in a sorted order and do a binary search. Or you could store your keywords in a Trie data structure (something like 26-ary tree) to search for words. Hope this helps :)
In a C99+SDL game, I have an array that contains sound effects (SDL_mixer chunk data and some extra flags and filename string) and is referenced by index such as "sounds[2].data".
I'd like to be able to call sounds by filename, but I don't want to strcmp all the array until a match is found. This way as I add more sounds, or change the order, or allow for player-defined sound mods, they can still be called with a common identifier (such as "SHOT01" or "EXPL04").
What would be the fastest approach for this? I heard about hashing, which would result in something similar to lua's string indexes (such as table["field"]) but I don't know anything about the topic, and seems fairly complicated.
Just in case it matters, I plan to have filenames or labels be from 6 to 8 all caps filenames (such as "SHOT01.wav").
So to summarize, where can I learn about hashing short strings like that, or what would be the fastest way to keep track of something like sound effects so they can be called using arbitrary labels or identifiers?
I think in your case you can probably just keep all the sounds in a sorted data structure and use a fast search algorithm to find matches. Something like a binary search is very simple implement and it gives good performance.
However, if you are interested in hash tables and hashing, the basics of it all are pretty simple. There is no place like Wikipedia to get the basics down and you can then tailor your searches better on Google to find more in depth articles.
The basics are you start out with a fixed size array and store everything in there. To figure out where to store something you take the key (in your case the sound name) and you perform some operation on it such that it gives you an exact location where the value can be found. So the simplest case for string hashing is just adding up all the letters in the string as integer values then take the value and use modulus to give you an index in your array.
position = SUM(string letters) % [array size]
Of course naturally multiple strings will have same sum and thus give you the same position. This is called a collision, and collisions can be handled in many ways. The simplest way is to have an array of lists rather than array of values, and simply append to the list every there there is a collision. When searching for a value, simply iterate the lists and find the value you need.
Ideally a good hashing algorithm will have few collisions and quick hashing algorithm thus providing huge performance boost.
I hope this helps :)
You are right, when it comes to mapping objects with a set of string keys, hash tables are often the way to go.
I think this article on wikipedia is a good starting point to understand hash table mechanism: http://en.wikipedia.org/wiki/Hash_table
How can we find the most efficient hash function(least possible chances of collision) for the set of strings.
Suppose we are given with some strings.. And the length of the strings is also not defined.
Ajay
Vijay
Rakhi
....
we know the count of no. of strings available, so we can design a hash table of size(count available). what could be the perfect hash function that we could design for such problem??
Multiplying each character ascii value by 31(prime no.) in increment fashion leads to the a hash value greater than the value of MAX_INT, and then modulus would not work properly... So please give some efficient hash function build up solution....
I have few set of strings,, lets say count = 10.... I need to implement a hash function such that all those 10 strings fit in uniquely in the hash table.... Any perfect hash function O(1) available, for this kind of problem?? hash table size will be 10, for this case...
Only C Programming...
Please explain the logic at website.... http://burtleburtle.net/bob/c/perfect.c
This looks very complicated but perfect to me..!! what is the algorithm used here... Reading the code straight away, is very difficult!!
Thanks....
Check some of these out, they apparantly have good distributions
http://www.partow.net/programming/hashfunctions/#HashingMethodologies
You might want to look into perfect hashing.
you might want to have a look at gperf, you could kinda do this on the fly if you didn't do it too often and your data set a small. if the strings are know ahead of time, then this is the method
Hash tables are meant to be able to handle dynamic input. If you can guarantee only a particular set of inputs, and you want to guarantee a particular slot for each input, why hash at all?
Just make an array indexed for each known available input.