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How to use a regular expression to search for sequential repetition in a string (ie [12] [12]), but only 2 or more in length?

import java.util.regex.Matcher; import java.util.regex.Pattern; public class test { public static void main(String[] args) { String a ="12341234"; String regex="^(\\d+?)\\1$"; Pattern p=Pattern.compile(regex); Matcher matcher = p.matcher(a); while(matcher.find()) { System.out.println(matcher.group(1)); } } }

Using Matcher and the regex above, I get any repetition. However, I only need replays of size 2 or higher. When I tried to make a regex

 ^(\\d+?){2,100}\\1$

nothing was returned when I ran the program, although there was a repeat between length 2 and 100. What am I doing wrong?

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2 answers

Your idea is correct, you just need to fix it a bit. Try the following:

 (\d{2,100})\1

I tested [here]

Update for HSCoder request:

make sure the repeated sequence doesn't have two consecutive numbers the same? For example, [11] [11] will not work, but [12] [12] will

Well, it really hurts to get every two consecutive numbers that are different from each other. Try the following:

 ((?:(?=0[^0]|1[^1]|2[^2]|3[^3]|4[^4]|5[^5]|6[^6]|7[^7]|8[^8]|9[^9])\d)+\d)\1

I tested [here]

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Description

 ([0-9]{2,})\1+

Regular expression visualization

This regex will do the following:

  • Find substrings consisting of two or more digits repeating 1 or more times in a row.

Example

Live demo

https://regex101.com/r/cA5qB7/1

Sample text

 22222 1111 2323 12341234 123123123123 123123123 1 11 1212 14 14 12345

Matching Examples

  • Capture group 0 gets the entire matched row, including all retries
  • Capture Group 1 receives a substring
 [0][0] = 2222 [0][1] = 22 [1][0] = 1111 [1][1] = 11 [2][0] = 2323 [2][1] = 23 [3][0] = 12341234 [3][1] = 1234 [4][0] = 123123123123 [4][1] = 123123 [5][0] = 123123123 [5][1] = 123 [6][0] = 1212 [6][1] = 12

Explanation

 NODE EXPLANATION ---------------------------------------------------------------------- ( group and capture to \1: ---------------------------------------------------------------------- [0-9]{2,} any character of: '0' to '9' (at least 2 times (matching the most amount possible)) ---------------------------------------------------------------------- ) end of \1 ---------------------------------------------------------------------- \1+ what was matched by capture \1 (1 or more times (matching the most amount possible)) ----------------------------------------------------------------------
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