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Fix typo #3837

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Fix typo 
this formula should be 2^(n-1)
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@bangjiehan
bangjiehan authored Apr 18, 2025
commit bc4a2fa657968416f0accd9e8277b0b0ed1a3639
8 changes: 4 additions & 4 deletions 9-regular-expressions/15-regexp-catastrophic-backtracking/article.md
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Expand Up @@ -150,11 +150,11 @@ Here's what the regexp engine does:
...And so on.


There are many ways to split a sequence of digits `123456789` into numbers. To be precise, there are <code>2<sup>n</sup>-1</code>, where `n` is the length of the sequence.
There are many ways to split a sequence of digits `123456789` into numbers. To be precise, there are <code>2<sup>n-1</sup></code>, where `n` is the length of the sequence.

- For `123456789` we have `n=9`, that gives 511 combinations.
- For a longer sequence with `n=20` there are about one million (1048575) combinations.
- For `n=30` - a thousand times more (1073741823 combinations).
- For `123456789` we have `n=9`, that gives 256 combinations.
- For a longer sequence with `n=21` there are about one million (1048576) combinations.
- For `n=31` - a thousand times more (1073741824 combinations).

Trying each of them is exactly the reason why the search takes so long.

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