He's building a regex which is trying to match n numbers, because of the (fail) it keeps backtracking to match all possibilities.

The embedded Perl code ensures the output before backtracking to the next match.

I actual like seeing such code as answers to lazy questions. ;)

In reply to Re^3: Sum of N elements in an M element array by Anonymous Monk
in thread Sum of N elements in an M element array by abhay180

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