I have strings like ABCBBBCBADBCCACDDDAC that represent 5x4 grids that could be displayed like:

A B C B B
B C B A D
B C C A C
D D D A C

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I have millions of strings corresponding to various (known) sizes from 4x4 to 10x12 and dozens of patterns to recognize on each grid/string. I could split/unpack the string to an array or AoA, but regexes actually work very well in my case, and they're much faster than looping over arrays. Well, almost. Say I want to match horizontal runs of 3 of the same character. Easy, right?

/(.)\1\1/

Wrong! This matches the D D D in the last row, but also incorrectly matches the B B + B split between rows 1 and 2. How would I (efficiently) match the D D D but not the B B B? All of my other patterns work efficiently with the unmodified string (several of them can even be combined into one expression), so if you do suggest an alternate storage format for the string, please also consider the cost of the conversion when thinking about efficiency, here.

In reply to Regex matching on grid alignment by Anonymous Monk

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