mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-11-27 23:11:09 +00:00
07e991d553
* ci(pre-commit): Add pep8-naming to `pre-commit` hooks (#7038) * refactor: Fix naming conventions (#7038) * Update arithmetic_analysis/lu_decomposition.py Co-authored-by: Christian Clauss <cclauss@me.com> * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * refactor(lu_decomposition): Replace `NDArray` with `ArrayLike` (#7038) * chore: Fix naming conventions in doctests (#7038) * fix: Temporarily disable project euler problem 104 (#7069) * chore: Fix naming conventions in doctests (#7038) Co-authored-by: Christian Clauss <cclauss@me.com> Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
87 lines
2.7 KiB
Python
87 lines
2.7 KiB
Python
"""
|
|
The algorithm finds the pattern in given text using following rule.
|
|
|
|
The bad-character rule considers the mismatched character in Text.
|
|
The next occurrence of that character to the left in Pattern is found,
|
|
|
|
If the mismatched character occurs to the left in Pattern,
|
|
a shift is proposed that aligns text block and pattern.
|
|
|
|
If the mismatched character does not occur to the left in Pattern,
|
|
a shift is proposed that moves the entirety of Pattern past
|
|
the point of mismatch in the text.
|
|
|
|
If there no mismatch then the pattern matches with text block.
|
|
|
|
Time Complexity : O(n/m)
|
|
n=length of main string
|
|
m=length of pattern string
|
|
"""
|
|
from __future__ import annotations
|
|
|
|
|
|
class BoyerMooreSearch:
|
|
def __init__(self, text: str, pattern: str):
|
|
self.text, self.pattern = text, pattern
|
|
self.textLen, self.patLen = len(text), len(pattern)
|
|
|
|
def match_in_pattern(self, char: str) -> int:
|
|
"""finds the index of char in pattern in reverse order
|
|
|
|
Parameters :
|
|
char (chr): character to be searched
|
|
|
|
Returns :
|
|
i (int): index of char from last in pattern
|
|
-1 (int): if char is not found in pattern
|
|
"""
|
|
|
|
for i in range(self.patLen - 1, -1, -1):
|
|
if char == self.pattern[i]:
|
|
return i
|
|
return -1
|
|
|
|
def mismatch_in_text(self, current_pos: int) -> int:
|
|
"""
|
|
find the index of mis-matched character in text when compared with pattern
|
|
from last
|
|
|
|
Parameters :
|
|
current_pos (int): current index position of text
|
|
|
|
Returns :
|
|
i (int): index of mismatched char from last in text
|
|
-1 (int): if there is no mismatch between pattern and text block
|
|
"""
|
|
|
|
for i in range(self.patLen - 1, -1, -1):
|
|
if self.pattern[i] != self.text[current_pos + i]:
|
|
return current_pos + i
|
|
return -1
|
|
|
|
def bad_character_heuristic(self) -> list[int]:
|
|
# searches pattern in text and returns index positions
|
|
positions = []
|
|
for i in range(self.textLen - self.patLen + 1):
|
|
mismatch_index = self.mismatch_in_text(i)
|
|
if mismatch_index == -1:
|
|
positions.append(i)
|
|
else:
|
|
match_index = self.match_in_pattern(self.text[mismatch_index])
|
|
i = (
|
|
mismatch_index - match_index
|
|
) # shifting index lgtm [py/multiple-definition]
|
|
return positions
|
|
|
|
|
|
text = "ABAABA"
|
|
pattern = "AB"
|
|
bms = BoyerMooreSearch(text, pattern)
|
|
positions = bms.bad_character_heuristic()
|
|
|
|
if len(positions) == 0:
|
|
print("No match found")
|
|
else:
|
|
print("Pattern found in following positions: ")
|
|
print(positions)
|