94 lines
2.0 KiB
Python
94 lines
2.0 KiB
Python
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#!/usr/bin/python
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# -*- coding: UTF-8 -*-
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from time import time
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def bf(main, pattern):
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"""
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字符串匹配，bf暴搜
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:param main: 主串
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:param pattern: 模式串
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:return:
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"""
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n = len(main)
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m = len(pattern)
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if n <= m:
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return 0 if pattern == main else -1
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for i in range(n-m+1):
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for j in range(m):
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if main[i+j] == pattern[j]:
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if j == m-1:
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return i
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else:
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continue
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else:
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break
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return -1
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def simple_hash(s, start, end):
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"""
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计算子串的哈希值
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每个字符取acs-ii码后求和
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:param s:
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:param start:
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:param end:
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:return:
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"""
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assert start <= end
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ret = 0
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for c in s[start: end+1]:
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ret += ord(c)
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return ret
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def rk(main, pattern):
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n = len(main)
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m = len(pattern)
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if n <= m:
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return 0 if pattern == main else -1
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# 子串哈希值表
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hash_memo = [None] * (n-m+1)
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hash_memo[0] = simple_hash(main, 0, m-1)
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for i in range(1, n-m+1):
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hash_memo[i] = hash_memo[i-1] - simple_hash(main, i-1, i-1) + simple_hash(main, i+m-1, i+m-1)
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# 模式串哈希值
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hash_p = simple_hash(pattern, 0, m-1)
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for i, h in enumerate(hash_memo):
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# 可能存在哈希冲突
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if h == hash_p:
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if pattern == main[i:i+m]:
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return i
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else:
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continue
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return -1
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if __name__ == '__main__':
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m_str = 'a'*10000
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p_str = 'a'*200+'b'
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print('--- time consume ---')
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t = time()
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print('[bf] result:', bf(m_str, p_str))
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print('[bf] time cost: {0:.5}s'.format(time()-t))
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t = time()
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print('[rk] result:', rk(m_str, p_str))
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print('[rk] time cost: {0:.5}s'.format(time()-t))
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print('')
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print('--- search ---')
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m_str = 'thequickbrownfoxjumpsoverthelazydog'
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p_str = 'jump'
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print('[bf] result:', bf(m_str, p_str))
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print('[rk] result:', rk(m_str, p_str))
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