If that were to fail to match, then it would fail to match very badly, as in O(N**K) badly. Better: 

/^[^a]*?a[^b]*?b[^c]*?c[^d]*?d/

[download]

or use features that I don't use and so don't remember to prevent backtracking. The above version should proceed to match the string linearly and in O(n) and, if that fails, backtrack linearly in O(n) and quickly fail.

- tye        

In reply to Re^3: Can KMP be used to find the longest common subsequence? (ugh) by tye
in thread Can KMP be used to find the longest common subsequence? by Anonymous Monk

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