Regular expressions and string matching

[DennyLoi]

Hi everyone,

Here is my problem, I have a partially decrypted piece string which would appear something like.

Partially deycrpted: the?anage??esideshe?e
Plain text: themanagerresideshere


So you can see that there are a few letter missing from the decryped text. What I am trying to do it insert spaces into the string so that I get:

The ?anage? ?esides he?e

I have a method which splits up the string in substrings of varying lengths and then compares the substring with a word from a dictionary (implemented as an arraylist) and then inserts a space.

The problem is that my function does not find the words in the dictionary because my string is only partially decryped.

Eg: ?anage? is not stored in the dictionary, but the word “manager” is.

So my question is, is there a way to build a regular expression which would match the partially decrypted text with a word from a dictionary (ie - ?anage? is recognised and “manager” from the dictionary).

[JosAH]

So my question is, is there a way to build a regular expression which would match the partially decrypted text with a word from a dictionary (ie - ?anage? is recognised and “manager” from the dictionary).

Yes you can do that: the regular expression ".anage." matches "manager" but
you have to check all your words in your dictionary for a possible match which
can be quite slow. Google for "PATRICIA" trie and see how this can be done a
bit more clever. Your dictionary needs probably be changed structurally for that.

kind regards,

Jos

[r035198x]

Hi everyone,

Here is my problem, I have a partially decrypted piece string which would appear something like.

Partially deycrpted: the?anage??esideshe?e
Plain text: themanagerresideshere


So you can see that there are a few letter missing from the decryped text. What I am trying to do it insert spaces into the string so that I get:

The ?anage? ?esides he?e

I have a method which splits up the string in substrings of varying lengths and then compares the substring with a word from a dictionary (implemented as an arraylist) and then inserts a space.

The problem is that my function does not find the words in the dictionary because my string is only partially decryped.

Eg: ?anage? is not stored in the dictionary, but the word “manager” is.

So my question is, is there a way to build a regular expression which would match the partially decrypted text with a word from a dictionary (ie - ?anage? is recognised and “manager” from the dictionary).

The * wildcard is your friend here. You can read more about it.

[JosAH]

The * wildcard is your friend here. You can read more about it.

Erm, make that a dot instead of a star. Regular expressions are not globbing.

kind regards,

Jos

[r035198x]

Erm, make that a dot instead of a star. Regular expressions are not globbing.

kind regards,

Jos

No they are not.
. it is.
From my very own link!

These leaves us with:

• Replace any * characters with .*
• Replace any ? characters with .
• Leave square brackets as they are.
• Replace any characters which are metacharacters with a backslashified version.

[JosAH]

No they are not.
. it is.
From my very own link!

Hrmph; your quote is gone in my reply; but that's not how Posix regular expressions
work: a dot is a single char that matches anything and a star is a reflexive closure
of the previous regular expression (i.e. the regex to the left of it). What you described
resembles a globbing pattern to a regular expression conversion.

kind regards,

Jos

[r035198x]

...What you described
resembles a globbing pattern to a regular expression conversion.

kind regards,

Jos

That's what was being explained at the point that I extracted.
Which is what I should have done(the conversion that is).

[DennyLoi]

I wrote the following method in order to test the matching using . in my regular expression.

public void getWords(int y)
{
int x = 0;
for(y=y; y < buff.length(); y++){
String strToCompare = buff.substring(x,y); //where buff holds the partially decrypted text
x++;
Pattern p = Pattern.compile(strToCompare);
for(int z = 0; z < dict.size(); z++){
String str = (String) dict.get(z); //where dict hold all the words in the dictionary
Matcher m = p.matcher(str);
if(m.matches()){
System.out.println(str);
System.out.println(strToCompare);
}}}
// System.out.println(buff);
}

If I run the method where my parameter = 12, I am given the following output.

aestheticism
aestheti.is.
demographics
de.o.ra.....

Which suggests that the method is working correctly.

However, after running for a short time, the method cuts and gives me the error:
PatternSyntaxException:
Null(in java.util.regex.Pattern).

Does anyone know why this would occur?