algorithm-test/src/bm.py

from typing import Dict


def make_km_table(pattern: str) -> Dict[str, int]:
    PATTERN_LENGTH = len(pattern)
    table = {}
    for index_from_left, char in enumerate(pattern[:-1]):
        table[char] = PATTERN_LENGTH - index_from_left - 1
    return table


class Bm(object):
    def __init__(self, text: str, pattern: str):
        self.text = text
        self.pattern = pattern
        self.table = make_km_table(pattern)

    def decide_slide_width(self, c: str) -> int:
        try:
            return self.table[c]
        except KeyError:
            return len(self.pattern)

    def search(self) -> int:
        PATTERN_LENGTH = len(self.pattern)
        head = PATTERN_LENGTH - 1
        while head < len(self.text):
            if self.text[head] == self.pattern[-1]:
                for index_from_right, char in enumerate(reversed(self.pattern)):
                    if self.text[head - index_from_right] != char:
                        head += self.decide_slide_width(self.text[head])
                        break
                else:
                    return head - PATTERN_LENGTH + 1
            else:
                head += self.decide_slide_width(self.text[head])
        return -1