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61 lines
2.1 KiB
C++
61 lines
2.1 KiB
C++
#pragma once
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#include <cstdint>
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#include <string>
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namespace coding
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{
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// Computes the Burrows-Wheeler transform of the string |s|, stores
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// result in the string |r|. Note - the size of |r| must be |n|.
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// Returns the index of the original string among the all sorted
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// rotations of the |s|.
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//
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// *NOTE* in contrast to popular explanations of BWT, we do not append
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// to |s| trailing '$' that is less than any other character in |s|.
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// The reason is that |s| can be an arbitrary byte string, with zero
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// bytes inside, so implementation of this trailing '$' is expensive,
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// and, actually, not needed.
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//
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// For example, if |s| is "abaaba", canonical BWT is:
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//
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// Sorted rotations: canonical BWT:
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// $abaaba a
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// a$abaab b
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// aaba$ab b
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// aba$aba a
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// * abaaba$ $
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// ba$abaa a
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// baaba$a a
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//
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// where '*' denotes original string.
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//
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// Our implementation will sort rotations in a way as there is an
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// implicit '$' that is less than any other byte in |s|, but does not
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// return this '$'. Therefore, the order of rotations will be the same
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// as above, without the first '$abaaba':
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//
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// Sorted rotations: ours BWT:
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// aabaab b
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// aabaab b
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// abaaba a
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// * abaaba a
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// baabaa a
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// baabaa a
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//
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// where '*' denotes the index of original string. As one can see,
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// there are two 'abaaba' strings, but as mentioned, rotations are
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// sorted like there is an implicit '$' at the end of the original
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// string. It's possible to get from "ours BWT" to the "original BWT",
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// see the code for details.
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//
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// Complexity: O(n) time and O(n) memory.
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size_t BWT(size_t n, uint8_t const * s, uint8_t * r);
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size_t BWT(std::string const & s, std::string & r);
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// Inverse Burrows-Wheeler transform.
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//
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// Complexity: O(n) time and O(n) memory.
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void RevBWT(size_t n, size_t start, uint8_t const * s, uint8_t * r);
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void RevBWT(size_t start, std::string const & s, std::string & r);
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} // namespace coding
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