mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-11-24 05:21:09 +00:00
e3eb9daba4
* Add bitap_string_match algo * Fix types * Fix spelling and add ignore word * Add suggested changes and change return type * Resolve suggestions
80 lines
2.3 KiB
Python
80 lines
2.3 KiB
Python
"""
|
|
Bitap exact string matching
|
|
https://en.wikipedia.org/wiki/Bitap_algorithm
|
|
|
|
Searches for a pattern inside text, and returns the index of the first occurrence
|
|
of the pattern. Both text and pattern consist of lowercase alphabetical characters only.
|
|
|
|
Complexity: O(m*n)
|
|
n = length of text
|
|
m = length of pattern
|
|
|
|
Python doctests can be run using this command:
|
|
python3 -m doctest -v bitap_string_match.py
|
|
"""
|
|
|
|
|
|
def bitap_string_match(text: str, pattern: str) -> int:
|
|
"""
|
|
Retrieves the index of the first occurrence of pattern in text.
|
|
|
|
Args:
|
|
text: A string consisting only of lowercase alphabetical characters.
|
|
pattern: A string consisting only of lowercase alphabetical characters.
|
|
|
|
Returns:
|
|
int: The index where pattern first occurs. Return -1 if not found.
|
|
|
|
>>> bitap_string_match('abdabababc', 'ababc')
|
|
5
|
|
>>> bitap_string_match('aaaaaaaaaaaaaaaaaa', 'a')
|
|
0
|
|
>>> bitap_string_match('zxywsijdfosdfnso', 'zxywsijdfosdfnso')
|
|
0
|
|
>>> bitap_string_match('abdabababc', '')
|
|
0
|
|
>>> bitap_string_match('abdabababc', 'c')
|
|
9
|
|
>>> bitap_string_match('abdabababc', 'fofosdfo')
|
|
-1
|
|
>>> bitap_string_match('abdab', 'fofosdfo')
|
|
-1
|
|
"""
|
|
if not pattern:
|
|
return 0
|
|
m = len(pattern)
|
|
if m > len(text):
|
|
return -1
|
|
|
|
# Initial state of bit string 1110
|
|
state = ~1
|
|
# Bit = 0 if character appears at index, and 1 otherwise
|
|
pattern_mask: list[int] = [~0] * 27 # 1111
|
|
|
|
for i, char in enumerate(pattern):
|
|
# For the pattern mask for this character, set the bit to 0 for each i
|
|
# the character appears.
|
|
pattern_index: int = ord(char) - ord("a")
|
|
pattern_mask[pattern_index] &= ~(1 << i)
|
|
|
|
for i, char in enumerate(text):
|
|
text_index = ord(char) - ord("a")
|
|
# If this character does not appear in pattern, it's pattern mask is 1111.
|
|
# Performing a bitwise OR between state and 1111 will reset the state to 1111
|
|
# and start searching the start of pattern again.
|
|
state |= pattern_mask[text_index]
|
|
state <<= 1
|
|
|
|
# If the mth bit (counting right to left) of the state is 0, then we have
|
|
# found pattern in text
|
|
if (state & (1 << m)) == 0:
|
|
return i - m + 1
|
|
|
|
return -1
|
|
|
|
|
|
if __name__ == "__main__":
|
|
import doctest
|
|
|
|
doctest.testmod()
|