How Can I Find Overlapping Regex Matches in a String?

Find overlapping regular expression matches

Suppose you need to find all occurrences of a pattern in a string, even if those occurrences overlap each other. For example, given the string "nnnn", you want to identify the following matches:

<code>nn
nnn
nnn</code>

While regular expressions are not inherently designed for this kind of overlap matching, there are some potential solutions:

Looking backward

One approach involves using forward lookbehind assertions, denoted as (?<=...)

Look forward

A more direct and intuitive method is to use forward lookahead assertion: (?=nn)n. This pattern looks for the presence of "nn" after the current "n" characters, resulting in a match at the beginning of each "nn" sequence.

Combining look-ahead and capture

Another approach is to combine forward lookahead with capturing parentheses: (n)(?=(n)). This formula captures the first "n" in group(1) and the second "n" in group(2), providing greater flexibility for matching complex patterns.

By using these techniques, you can efficiently find overlapping matches in regular expression patterns, even if they deviate from the usual purpose of regular expressions.

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