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"""

https://en.wikipedia.org/wiki/Burrows%E2%80%93Wheeler_transform

The Burrows–Wheeler transform (BWT, also called block-sorting compression)

rearranges a character string into runs of similar characters. This is useful

for compression, since it tends to be easy to compress a string that has runs

of repeated characters by techniques such as move-to-front transform and

run-length encoding. More importantly, the transformation is reversible,

without needing to store any additional data except the position of the first

original character. The BWT is thus a "free" method of improving the efficiency

of text compression algorithms, costing only some extra computation.

"""

from typing import List, Dict

def all_rotations(s: str) -> List[str]:

"""

:param s: The string that will be rotated len(s) times.

:return: A list with the rotations.

:raises TypeError: If s is not an instance of str.

Examples:

>>> all_rotations("^BANANA|") # doctest: +NORMALIZE_WHITESPACE

'A|^BANAN', '|^BANANA']

>>> all_rotations("a_asa_da_casa") # doctest: +NORMALIZE_WHITESPACE

['a_asa_da_casa', '_asa_da_casaa', 'asa_da_casaa_', 'sa_da_casaa_a',

'a_da_casaa_as', '_da_casaa_asa', 'da_casaa_asa_', 'a_casaa_asa_d',

'_casaa_asa_da', 'casaa_asa_da_', 'asaa_asa_da_c', 'saa_asa_da_ca',

'aa_asa_da_cas']

>>> all_rotations("panamabanana") # doctest: +NORMALIZE_WHITESPACE

['panamabanana', 'anamabananap', 'namabananapa', 'amabananapan',

'mabananapana', 'abananapanam', 'bananapanama', 'ananapanamab',

'nanapanamaba', 'anapanamaban', 'napanamabana', 'apanamabanan']

>>> all_rotations(5)

Traceback (most recent call last):

...

TypeError: The parameter s type must be str.

"""

if not isinstance(s, str):

raise TypeError("The parameter s type must be str.")

return [s[i:] + s[:i] for i in range(len(s))]

def bwt_transform(s: str) -> Dict:

"""

:param s: The string that will be used at bwt algorithm

:return: the string composed of the last char of each row of the ordered

rotations and the index of the original string at ordered rotations list

:raises TypeError: If the s parameter type is not str

:raises ValueError: If the s parameter is empty

Examples:

>>> bwt_transform("^BANANA")

{'bwt_string': 'BNN^AAA', 'idx_original_string': 6}

>>> bwt_transform("a_asa_da_casa")

{'bwt_string': 'aaaadss_c__aa', 'idx_original_string': 3}

>>> bwt_transform("panamabanana")

{'bwt_string': 'mnpbnnaaaaaa', 'idx_original_string': 11}

>>> bwt_transform(4)

Traceback (most recent call last):

...

TypeError: The parameter s type must be str.

>>> bwt_transform('')

Traceback (most recent call last):

...

ValueError: The parameter s must not be empty.

"""

if not isinstance(s, str):

raise TypeError("The parameter s type must be str.")

if not s:

raise ValueError("The parameter s must not be empty.")

rotations = all_rotations(s)

rotations.sort() # sort the list of rotations in alphabetically order

# make a string composed of the last char of each rotation

return {

"bwt_string": "".join([word[-1] for word in rotations]),

"idx_original_string": rotations.index(s),

}

def reverse_bwt(bwt_string: str, idx_original_string: int) -> str:

"""

:param bwt_string: The string returned from bwt algorithm execution

:param idx_original_string: A 0-based index of the string that was used to

generate bwt_string at ordered rotations list

:return: The string used to generate bwt_string when bwt was executed

:raises TypeError: If the bwt_string parameter type is not str

:raises ValueError: If the bwt_string parameter is empty

:raises TypeError: If the idx_original_string type is not int or if not

possible to cast it to int

:raises ValueError: If the idx_original_string value is lower than 0 or

greater than len(bwt_string) - 1

>>> reverse_bwt("BNN^AAA", 6)

'^BANANA'

>>> reverse_bwt("aaaadss_c__aa", 3)

'a_asa_da_casa'

>>> reverse_bwt("mnpbnnaaaaaa", 11)

'panamabanana'

>>> reverse_bwt(4, 11)

Traceback (most recent call last):

...

TypeError: The parameter bwt_string type must be str.

>>> reverse_bwt("", 11)

Traceback (most recent call last):

...

ValueError: The parameter bwt_string must not be empty.

>>> reverse_bwt("mnpbnnaaaaaa", "asd") # doctest: +NORMALIZE_WHITESPACE

Traceback (most recent call last):

...

TypeError: The parameter idx_original_string type must be int or passive

of cast to int.

>>> reverse_bwt("mnpbnnaaaaaa", -1)

Traceback (most recent call last):

...

ValueError: The parameter idx_original_string must not be lower than 0.

>>> reverse_bwt("mnpbnnaaaaaa", 12) # doctest: +NORMALIZE_WHITESPACE

Traceback (most recent call last):

...

ValueError: The parameter idx_original_string must be lower than

len(bwt_string).

>>> reverse_bwt("mnpbnnaaaaaa", 11.0)

'panamabanana'

>>> reverse_bwt("mnpbnnaaaaaa", 11.4)

'panamabanana'

"""

if not isinstance(bwt_string, str):

raise TypeError("The parameter bwt_string type must be str.")

if not bwt_string:

raise ValueError("The parameter bwt_string must not be empty.")

try:

idx_original_string = int(idx_original_string)

except ValueError:

raise TypeError(

"The parameter idx_original_string type must be int or passive"

" of cast to int."

)

if idx_original_string < 0:

raise ValueError("The parameter idx_original_string must not be lower than 0.")

if idx_original_string >= len(bwt_string):

raise ValueError(

"The parameter idx_original_string must be lower than" " len(bwt_string)."

)

ordered_rotations = [""] * len(bwt_string)

for x in range(len(bwt_string)):

for i in range(len(bwt_string)):

ordered_rotations[i] = bwt_string[i] + ordered_rotations[i]

ordered_rotations.sort()

return ordered_rotations[idx_original_string]

if __name__ == "__main__":

entry_msg = "Provide a string that I will generate its BWT transform: "

s = input(entry_msg).strip()

result = bwt_transform(s)

bwt_output_msg = "Burrows Wheeler tranform for string '{}' results in '{}'"

print(bwt_output_msg.format(s, result["bwt_string"]))

original_string = reverse_bwt(result["bwt_string"], result["idx_original_string"])

fmt = (

"Reversing Burrows Wheeler tranform for entry '{}' we get original"

" string '{}'"

)

print(fmt.format(result["bwt_string"], original_string))

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