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AK: Improve performance of StringUtils::find_last
The current algorithm is currently O(N^2) because we forward-search an ever-increasing substring of the haystack. This implementation reduces the search time of a 500,000-length string (where the desired needle is at index 0) from 72 seconds to 2-3 milliseconds.
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sideshowbarker
2024-07-17 08:35:21 +09:00
Author: https://github.com/trflynn89 Commit: https://github.com/SerenityOS/serenity/commit/cae184d7cf Pull-request: https://github.com/SerenityOS/serenity/pull/22562 Reviewed-by: https://github.com/nico ✅
@ -412,10 +412,15 @@ Optional<size_t> find_last(StringView haystack, char needle)
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Optional<size_t> find_last(StringView haystack, StringView needle)
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{
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for (size_t i = haystack.length(); i > 0; --i) {
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auto value = StringUtils::find(haystack, needle, i - 1);
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if (value.has_value())
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return value;
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if (needle.length() > haystack.length())
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return {};
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for (size_t i = haystack.length() - needle.length();; --i) {
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if (haystack.substring_view(i, needle.length()) == needle)
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return i;
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if (i == 0)
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break;
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}
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return {};
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