boyer-moore算法python

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Boyer-Moore算法是一种用于字符串搜索的高效算法，它通过跳过尽可能多的字符来减少比较的次数。下面是一个简单的Python实现Boyer-Moore算法的示例：

def build_bad_char_table(pattern):

    bad_char_table = {}

    pattern_length = len(pattern)

    for i in range(pattern_length - 1):

        bad_char_table[pattern[i]] = pattern_length - i - 1

    return bad_char_table

def build_good_suffix_table(pattern):

    pattern_length = len(pattern)

    good_suffix_table = [-1] * pattern_length

    last_prefix_position = pattern_length

    for i in range(pattern_length - 1, -1, -1):

        if is_prefix(pattern, i + 1):

            last_prefix_position = i + 1

        good_suffix_table[i] = last_prefix_position + pattern_length - i - 1

    for i in range(pattern_length - 1):

        j = pattern_length - 1 - i

        if is_suffix(pattern, j):

            last_prefix_position = j

        good_suffix_table[j] = min(good_suffix_table[j], pattern_length - 1 - last_prefix_position + j)

    return good_suffix_table

def is_prefix(pattern, p):

    pattern_length = len(pattern)

    j = 0

    for i in range(p, pattern_length):

        if pattern[i] != pattern[j]:

            return False

        j += 1

    return True

def is_suffix(pattern, p):

    pattern_length = len(pattern)

    i = 0

    j = p

    while j < pattern_length:

        if pattern[i] != pattern[j]:

            return False

        i += 1

        j += 1

    return True

def boyer_moore_search(text, pattern):

    bad_char_table = build_bad_char_table(pattern)

    good_suffix_table = build_good_suffix_table(pattern)

    pattern_length = len(pattern)

    text_length = len(text)

    i = 0

    while i <= text_length - pattern_length:

        j = pattern_length - 1

        while j >= 0 and pattern[j] == text[i + j]:

            j -= 1

        if j < 0:

            # Pattern found at index i

            print("Pattern found at index", i)

            i += good_suffix_table[0]

        else:

            # Shift based on the bad character rule and good suffix rule

            bad_char_shift = bad_char_table.get(text[i + j, -1])

            good_suffix_shift = good_suffix_table[j]

            i += max(bad_char_shift, good_suffix_shift)

# 测试Boyer-Moore搜索

text = "This is a sample text for testing the Boyer-Moore algorithm."

pattern = "Boyer-Moore"

boyer_moore_search(text, pattern)

这个示例包含了Boyer-Moore算法的实现，包括构建坏字符表（bad character table）和好后缀表（good suffix table）。然后，boyer_moore_search函数使用这些表来执行搜索。在这个示例中，它会输出找到的模式的索引位置。你可以将text和pattern更改为你自己的文本和模式来测试不同的输入。

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