#!/urs/bin/env python
# -*- coding:utf-8 -*- #异常类
class stringTypeError(TypeError):
pass #节点类
class Node(object):
def __init__(self, elem, next_ = None):
self.elem = elem
self.next = next_
#单链表类
class single_list(object):
def __init__(self):
self._head = None
self._num = 0 def __len__(self):
return self._num def prepend(self,elem):
self._head = Node(elem, self._head)
self._num += 1 def append(self,elem):
if self._head is None:
self._head = Node(elem)
self._num += 1
return
p = self._head
while p.next:
p = p.next
p.next = Node(elem)
self._num += 1 def pop_last(self):
if self._head is None:
raise ValueError("in pop_last")
p = self._head
if p.next is None:
e = p.elem
self._head = None
self._num -= 1
return e
while p.next.next:
p = p.next
e = p.next.elem
p.next = None
self._num -= 1
return e def delitem(self, key):
if key == len(self)-1:
self.pop_last()
elif 0<= key < len(self) - 1:
p = self._head
pre = None
num = -1
while p is not None:
num += 1
if key==num:
if not pre:
self._head = p.next
self._num -= 1
else:
pre.next = p.next
self._num -= 1
break
else:
pre = p
p = p.next
else:
raise IndexError def insert(self, key, elem):
if key>=len(self)-1:
self.append(elem)
elif 0<=key<len(self)-1:
p = self._head
pre = None
num = -1
while p:
num += 1
if num==key:
if not pre:
self._head = Node(elem, self._head)
self._num += 1
else:
pre.next = Node(elem, pre.next)
self._num += 1
break
else:
pre = p
p = p.next
else:
raise IndexError # 打印显示
def printall(self):
p = self._head
while p:
print(p.elem, end="")
if p.next:
print(", ", end="")
p = p.next
print("") #单链表字符串类
class string(single_list):
def __init__(self, value):
self.value = str(value)
single_list.__init__(self)
for i in range(len(self.value)-1,-1,-1):
self.prepend(self.value[i]) def length(self):
return self._num def printall(self):
p = self._head
print("字符串结构：",end="")
while p:
print(p.elem, end="")
if p.next:
print("-->", end="")
p = p.next
print("") #朴素的串匹配算法，返回匹配的起始位置
def naive_matching(self, p): #self为目标字符串，t为要查找的字符串
if not isinstance(self, string) and not isinstance(p, string):
raise stringTypeError
m, n = p.length(), self.length()
i, j = 0, 0
while i < m and j < n:
if p.value[i] == self.value[j]:#字符相同，考虑下一对字符
i, j = i+1, j+1
else: #字符不同，考虑t中下一个位置
i, j = 0, j-i+1
if i == m: #i==m说明找到匹配,返回其下标
return j-i
return -1 #kmp匹配算法，返回匹配的起始位置
def matching_KMP(self, p):
j, i = 0, 0
n, m = self.length(), p.length()
while j < n and i < m:
if i == -1 or self.value[j] == p.value[i]:
j, i = j + 1, i + 1
else:
i = string.gen_next(p)[i]
if i == m:
return j - i
return -1 # 生成pnext表
@staticmethod
def gen_next(p):
i, k, m = 0, -1, p.length()
pnext = [-1] * m
while i < m - 1:
if k == -1 or p.value[i] == p.value[k]:
i, k = i + 1, k + 1
pnext[i] = k
else:
k = pnext[k]
return pnext #把old字符串出现的位置换成new字符串
def replace(self, old, new):
if not isinstance(self, string) and not isinstance(old, string) \
and not isinstance(new, string):
raise stringTypeError #删除匹配的旧字符串
start = self.matching_KMP(old)
for i in range(old.length()):
self.delitem(start)
#末尾情况下时append追加的，顺序为正；而前面的地方插入为前插；所以要分情况
if start<self.length():
for i in range(new.length()-1, -1, -1):
self.insert(start,new.value[i])
else:
for i in range(new.length()):
self.insert(start,new.value[i]) if __name__=="__main__": a = string("abcda")
print("字符串长度：",a.length())
a.printall()
b = string("abcabaabcdabdabcda")
print("字符串长度：", b.length())
b.printall()
print("朴素算法_匹配的起始位置：",b.naive_matching(a),end=" ")
print("KMP算法_匹配的起始位置：",b.matching_KMP(a))
c = string("xu")
print("==")
b.replace(a,c)
print("替换后的字符串是：")
b.printall()
今天早上在继续实现replace时，发现一个严重的问题。在我初始化字符串string对象时，使用了self.value = str(value),而我在后面使用匹配算法时，无论是朴素匹配还是KMP匹配
都使用的对象的value值作为比较。所以对象实现replace方法后的start =b.mathcing_KMP(a)后依旧不变，会一直为6.原因在于我使用的是self.value在进行匹配。所以replace后的
链表字符串里的值并没有被利用到，从而发生严重的错误。
改进篇见下一篇博客