Merge pull request wangzheng0822#190 from KPatr1ck/bf_rk

BF & RK implementation in python

Author: wangzheng0822

python/32_bf_rk/bf_rk.py

@@ -0,0 +1,93 @@
+#!/usr/bin/python
+# -*- coding: UTF-8 -*-
+
+from time import time
+
+
+def bf(main, pattern):
+ """
+ 字符串匹配，bf暴搜
+ :param main: 主串
+ :param pattern: 模式串
+ :return:
+ """
+ n = len(main)
+ m = len(pattern)
+
+ if n <= m:
+ return 0 if pattern == main else -1
+
+ for i in range(n-m+1):
+ for j in range(m):
+ if main[i+j] == pattern[j]:
+ if j == m-1:
+ return i
+ else:
+ continue
+ else:
+ break
+ return -1
+
+
+def simple_hash(s, start, end):
+ """
+ 计算子串的哈希值
+ 每个字符取acs-ii码后求和
+ :param s:
+ :param start:
+ :param end:
+ :return:
+ """
+ assert start <= end
+
+ ret = 0
+ for c in s[start: end+1]:
+ ret += ord(c)
+ return ret
+
+
+def rk(main, pattern):
+ n = len(main)
+ m = len(pattern)
+
+ if n <= m:
+ return 0 if pattern == main else -1
+
+ # 子串哈希值表
+ hash_memo = [None] * (n-m+1)
+ hash_memo[0] = simple_hash(main, 0, m-1)
+ for i in range(1, n-m+1):
+ hash_memo[i] = hash_memo[i-1] - simple_hash(main, i-1, i-1) + simple_hash(main, i+m-1, i+m-1)
+
+ # 模式串哈希值
+ hash_p = simple_hash(pattern, 0, m-1)
+
+ for i, h in enumerate(hash_memo):
+ # 可能存在哈希冲突
+ if h == hash_p:
+ if pattern == main[i:i+m]:
+ return i
+ else:
+ continue
+ return -1
+
+
+if __name__ == '__main__':
+ m_str = 'a'*10000
+ p_str = 'a'*200+'b'
+
+ print('--- time consume ---')
+ t = time()
+ print('[bf] result:', bf(m_str, p_str))
+ print('[bf] time cost: {0:.5}s'.format(time()-t))
+
+ t = time()
+ print('[rk] result:', rk(m_str, p_str))
+ print('[rk] time cost: {0:.5}s'.format(time()-t))
+
+ print('')
+ print('--- search ---')
+ m_str = 'thequickbrownfoxjumpsoverthelazydog'
+ p_str = 'jump'
+ print('[bf] result:', bf(m_str, p_str))
+ print('[rk] result:', rk(m_str, p_str))