For a project that I'm currently working on I am dealing with a list of lists of integers, something of the form:
{[1,2];[5];[3,6,7]}
The idea here is that I'm trying to resolve an n-dimensional array into a list of the local maxima that occur in whatever particular axis I happen to be looking at. My question is this: I would like to get out a list of what would essentially be points in this n-dimensional space that contains every possible combination of entries of this list. For example, I would want the above to return:
{[1,5,3];[1,5,6];[1,5,7];[2,5,3];[2,5,6];[2,5,7]}
With the ordering not actually mattering to me. My first idea in how to approach this would be to boil this down to a tree where each path represents a possible combination and outputting every possible path, but I'm really not sure if this is the best way of going about it, and I am unfamiliar enough with Java's tree classes to be unsure if this would actually be straightforward to implement or not. Ideas?
Ah, my mistake, totally a duplicate.
Related
i'm writing some code, and I want my code to be well documented.
there is a part in the code where I'm checking that when there is a try to insert new element E to a list L, the element E will be unique (so there is no other elements in L that equals to him).
I'm having difficult to write a user-friendly mathematics comment, something that will look like the example bellow
the function will change all elements (that in list L) fields E.color to "Black" only if color to black element.size > 10.
so in that case I will write the comment -
[ X.color="Black" | X in L, X.size > 10]
but for the scenario above I couldnt find any satisfied mathmatics comment.
A mathematical set by definition has no duplicates inside it, so perhaps using the a set rather than a list would solve your problem.
However if that's too hard to change now then you could write something like:
[ L.insert(E) | E not in L ]
where E is the element and L is the list.
an exhaustive answer to your question requires two observations:
Best coding practices require you to know collections very well and when to use them. So you want the right collection for the right Job. In this case as advised in other comments, you need to use a Set instead of a list. A Set uses a Map under the hood, having your elements as keys and values as DEFAULT. Every time that you add an element to your Set, the Hash value for it is calculated and compared using equals to the existing elements. So no dups are allowed.
I really appreciate the fact that you want to write good comments, however you don't need to for the following reasons:
List and Sets behaviour is largely documented already, so nobody expects you to comment them;
Books like Refactoring and Clean code, teach us that good code should never be commented as it should be self explaining. That means that your method/class/variable name should tell me what the method is doing.
I'm making a chat responder for a game and i want know if there is a way you can compare two strings and see if they are approximatley equal to each other for example:
if someone typed:
"Strength level?"
it would do a function..
then if someone else typed:
"Str level?"
it would do that same function, but i want it so that if someone made a typo or something like that it would automatically detect what they're trying to type for example:
"Strength tlevel?"
would also make the function get called.
is what I'm asking here something simple or will it require me to make a big giant irritating function to check the Strings?
if you've been baffled by my explanation (Not really one of my strong points) then this is basically what I'm asking.
How can I check if two strings are similar to each other?
See this question and answer: Getting the closest string match
Using some heuristics and the Levenshtein distance algorithm, you can compute the similarity of two strings and take a guess at whether they're equal.
Your only option other than that would be a dictionary of accepted words similar to the one you're looking for.
You can use Levenshtein distance.
I believe you should use one of Edit distance algorithms to solve your problem. Here is for example Levenstein distance algorithm implementation in java. You may use it to compare words in the sentences and if sum of their edit distances would be less than for example 10% of sentence length consider them equals.
Perhaps what you need is a large dictionary for similar words and common spelling mistakes, for which you would use for each word to "translate" to one single entry or key.
This would be useful for custom words, so you could add "str" in the same key as "strength".
However, you could also make a few automated methods, i.e. when your word isn't found in the dictionary, to loop recursively for 1 letter difference (either missing or replaced) and can recurse into deeper levels, i.e. 2 missing letters etc.
I found a few projects that do text to phonemes translations, don't know which one is best
http://mary.dfki.de/
http://www2.eng.cam.ac.uk/~tpl/asp/source/Phoneme.java
http://java.dzone.com/announcements/announcing-phonemic-10
If you want to find similar word beginnings, you can use a stemmer. Stemmers reduce words to a common beginning. The most known algorithm if the Port Stemmer (http://tartarus.org/~martin/PorterStemmer).
Levenshtein, as pointed above, is great, but computational heavy for distances greater than one or two.
All the questions pertaining this don't seem to answer the particular question I have.
My problem is this. I have a list of search terms, and for each term I find the edit distance to find possible misspelling of a word.
So for each word separated by a space, I have possible words each word could be.
For example: searching for green chilli might give us "fuzzy" words "green, greene and grain" and "chilli, chill and chilly".
Now I want the RowFilter to search for: "green OR greene OR grain" AND "chilli OR chill OR chilly".
I can't seem to find a way to do this in Java. I've looked all over the place but nothing talks about concatenating the OR and AND filters together in one RowFilter.
Would I have to roll my own solution based on the model? I suppose I can do this, but my method would most probably be naive at first and slow.
Any pointers as to how to roll my own solution for this or better yet, what's the Java way to do this right?
RowFilter.orFilter() and RowFilter.andFilter() seem apropos; each includes examples, and each accepts an arbitrary number of arguments.
I have to keep in mind the priority of operations, all the numbers including the answer are integers (seems silly to me but whatever), and I have to parse a String for the equation and, as far as I'm aware, push each number and each operator in two different stacks before I compare them.
I don't know how to approach this problem, and right now my main concern is dealing with parentheses. I want to use a recursive method to solve the calculation which would check for parentheses and solve them and replace them with their result, but I'm not sure how to do that. I could use substring() and indexOf() but I'd rather be more elegant.
Other than that I'm not sure how to solve the calculation once numbers and operators are stacked. I think I should compare the top 2 operators to make sure that if I combine two numbers, it is in the right order of operations, but I don't want to be clumsy with that part either.
My recommendation would be that you study the Shunting-yard algorithm and come back when you have specific questions about how it works or how to implement certain parts of it.
Let's say I have a Java ArrayList, that is sorted. Now I would like to find the index of value x. What would be the fastest (without more than 30 lines of code) way to do this? Use of the IndexOf() method? Iterate through all values in a simple for loop? Use of some cool algorithm? We are talking about around let's say 50 integer keys.
Binary search, but since it's only 50 items, who cares (unless you have to do it millions of times)? A simple linear search is simpler and the difference in performance for 50 items is negligible.
Edit: You could also use the built-in java.util.Collections binarySearch method. Be aware, that it will return an insertion point even if the item isn't found. You may need to make an extra couple of checks to make sure that the item really is the one you want. Thanks to #Matthew for the pointer.
tvanfosson is right, that the time for either will be very low, so unless this code runs very frequently it won't make much difference.
However, Java has built-in functionality for binary searches of Lists (including ArrayLists), Collections.binarySearch.
import java.util.ArrayList;
import java.util.Collections;
ArrayList myList = new ArrayList();
// ...fill with values
Collections.sort( myList );
int index = Collections.binarySearch( myList, "searchVal" );
Edit: untested code
If the keys have a acceptable distribution, Interpolation Search might be very fast way considering execution time.
Considering coding time IndexOf() is the way to go (or a built-in in binary search if availiable for your data type (I am from C# and don't know Java)).