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from abc import ABCMeta, abstractmethod |
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class SubstringSearch(object): |
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__metaclass__ = ABCMeta |
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7
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@abstractmethod |
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def search_in(self, text): |
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pass |
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class BruteForceSubstringSearch(SubstringSearch): |
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def __init__(self, pattern): |
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self.pattern = pattern |
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def search_in(self, text): |
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n = len(text) |
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for i in range(n - len(self.pattern)): |
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J = i |
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for j in range(len(self.pattern)): |
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k = i + j |
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if text[k] != self.pattern[j]: |
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J = -1 |
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break |
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if J != -1: |
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return J |
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return -1 |
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def char_at(text, d): |
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return ord(text[d]) |
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35
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36
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class RabinKarp(SubstringSearch): |
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patHash = None |
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Q = 1573773197 |
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R = 256 |
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M = None |
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RM = None |
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def __init__(self, pat): |
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h = 1 |
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self.M = len(pat) |
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for i in range(1, self.M): |
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h = (h * RabinKarp.R) % RabinKarp.Q |
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self.RM = h |
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51
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self.patHash = self.hash(pat, self.M) |
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53
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def hash(self, text, M): |
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h = 0 |
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for d in range(M): |
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h = (h * RabinKarp.R + char_at(text, d)) % RabinKarp.Q |
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return h |
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59
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def search_in(self, text): |
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text_hash = self.hash(text, self.M) |
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if text_hash == self.patHash: |
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return 0 |
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for i in range(self.M, len(text)): |
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text_hash = (text_hash + RabinKarp.Q - self.RM * char_at(text, i - self.M) % RabinKarp.Q) % RabinKarp.Q |
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text_hash = (text_hash * RabinKarp.R + char_at(text, i)) % RabinKarp.Q |
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if text_hash == self.patHash: |
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return i - self.M + 1 |
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return -1 |
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70
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71
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class BoyerMoore(SubstringSearch): |
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right = None |
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R = 256 |
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pattern = None |
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def __init__(self, pattern): |
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self.pattern = pattern |
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self.right = [0] * BoyerMoore.R |
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for i in range(len(pattern)): |
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self.right[char_at(pattern, i)] = i |
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82
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def search_in(self, text): |
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n = len(text) |
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m = len(self.pattern) |
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86
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skip = 1 |
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i = 0 |
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while i <= n - m: |
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for j in range(m-1, -1, -1): |
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if char_at(text, i+j) != char_at(self.pattern, j): |
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skip = max(1, j - self.right[char_at(text, i+j)]) |
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break |
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if j == 0: |
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return i |
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i += skip |
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return -1 |
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99
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100
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class KnuthMorrisPratt(SubstringSearch): |
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102
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dfs = None |
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M = None |
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R = 256 |
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105
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106
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def __init__(self, pattern): |
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self.M = len(pattern) |
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108
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109
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self.dfs = [None] * self.R |
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for i in range(self.R): |
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self.dfs[i] = [0] * self.M |
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112
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self.dfs[0][0] = 1 |
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113
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114
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X = 0 |
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115
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for j in range(self.M): |
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for i in range(self.R): |
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self.dfs[i][j] = self.dfs[i][X] |
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self.dfs[char_at(pattern, j)][j] = j+1 |
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119
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X = self.dfs[char_at(pattern, j)][X] |
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120
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121
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def search_in(self, text): |
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123
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n = len(text) |
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124
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125
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j = 0 |
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126
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for i in range(n): |
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j = self.dfs[char_at(text, i)][j] |
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128
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if j == self.M: |
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return i - self.M |
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131
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return -1 |
chen0040 /
pyalgs
