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Copy pathstring_SStrings.py
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executable file
·97 lines (80 loc) · 2.57 KB
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# Naive string matching
# KMP 字符串匹配算法
def naive_matching(t, p):
j, i = 0, 0
n, m = len(t), len(p)
while j < n and i < m: # i==m means a matching
if t[j] == p[i]: # ok! consider next char in p
j, i = j + 1, i + 1
else: # no! consider next position in t
j, i = j - i + 1, 0
if i == m: # find a matching, return its index
return j - i
return -1 # no matching, return special value
## KMP string matching
# 关键，预处理模式串，得到匹配数组
def gen_pnext0(p):
""" Generate a list for the next checking index
"""
i, k, m = 0, -1, len(p)
pnext = [-1] * m
print(pnext)
while i < m - 1: # generate pnext[i+1]
while k >= 0 and p[i] != p[k]:
k = pnext[k]
i, k = i + 1, k + 1
pnext[i] = k # set a pnext entry
print('=>', pnext)
return pnext
# 关键，预处理模式串，得到匹配数组
# 优化的写法
def gen_pnext(p):
""" Generate a list for the next checking index,
a little revised version.
"""
i, k, m = 0, -1, len(p)
pnext = [-1] * m
print('=>', pnext)
while i < m - 1: # generate pnext[i+1]
while k >= 0 and p[i] != p[k]:
k = pnext[k]
i, k = i + 1, k + 1
if p[i] == p[k]: # 当两个字符相等时要跳过
pnext[i] = pnext[k]
else:
pnext[i] = k
print('=>', pnext)
return pnext
def KMPmatching(t, p, pnext):
""" KMP string mateching, the main function."""
j, i = 0, 0
n, m = len(t), len(p)
while j < n and i < m: # i==m means a matching
if i == -1 or t[j] == p[i]: # consider next char in p
j, i = j + 1, i + 1
else: # no! consider pnext char in p
i = pnext[i]
if i == m: # find a matching, return its index
return j - i
return -1 # no matching, return special value
def KMPmatching1(t, p, pnext):
""" KMP string matching, a little revised version."""
j, i = 0, 0
n, m = len(t), len(p)
while j < n and i < m: # i==m means a matching
while i >= 0 and t[j] != p[i]:
i = pnext[i]
j, i = j + 1, i + 1
if i == m: # find a matching, return its index
return j - i
return -1 # no matching, return special value
def matching(t, p):
return KMPmatching(t, p, gen_pnext0(p))
def matching1(t, p):
print(gen_pnext0(p))
return KMPmatching1(t, p, gen_pnext0(p))
t = "ABCDABEABC ABCDAB ABCDABCDABDE"
p = "ABCDABD"
if __name__ == '__main__':
gen_pnext(p)
# print(matching1(p))