CODEWITHSUNDEEP
javaregex
Marat Arguinbaev
Marat Arguinbaev

Reputation: 133

Java regex to find pattern of digits

Lets say I have a sequence of numbers

1 2 3 4 1 2 3 4

As you can see there is a cycle here:

1 2 3 4

Now I am trying to make a regex expression to match a pattern. The pattern can be half the length of the sequence or 2 numbers long. This is what I have so far 

Pattern cycle = Pattern.compile("((\\d+\\s)+(\\d+\\s))\\1");

I am given a string of numbers delimited by spaces. I am trying to use capture groups but not understanding it. Any help?

Upvotes: 0

Views: 4286

Answers (2)

angel_007
angel_007

Reputation: 103

I am just trying to understand the question better. Is your problem similar to detecting a cycle/pattern in a given string ?

Something similar to this pattern ?

 "([0-9]+?)\1+"

this pattern tries to capture a repeating pattern in a given stream of numbers.

Similar to the one discussed in this question What is wrong with my regex Pattern to find recurring cycles in Python?.

Upvotes: 0

fge
fge

Reputation: 121712

You can use this:

(\d(?:\s+\d)+)\s+\1

This will match two or more digits separated by spaces, capture it and look for what is captured right after another space character:

(            # begin capturing group
    \d       # a digit, followed by
    (?:      # begin non capturing group
        \s+  # one or more space characters, followed by
        \d   # a digit
    )+       # end non capturing group, repeated once or more,
)            # end capturing group `\1`, followed by
\s+          # one or more spaces, followed by
\1           # the exact content of the first captured group

Note: it assumes that the spacing is exactly the same in the repetition!

Upvotes: 3

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