From 3fd9a807194791012f244ee22bbd02f5d6e2965d Mon Sep 17 00:00:00 2001
From: gz1301 <109694228@qq.com>
Date: Wed, 12 Dec 2018 10:15:14 +0800
Subject: [PATCH] bf and rk in python

---
 python/32_bf_rk/bf_rk.py | 93 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)
 create mode 100644 python/32_bf_rk/bf_rk.py

diff --git a/python/32_bf_rk/bf_rk.py b/python/32_bf_rk/bf_rk.py
new file mode 100644
index 0000000..0cd2399
--- /dev/null
+++ b/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))