1 #!/urs/bin/env python
2 # -*- coding:utf-8 -*-
3
4 #异常类
5 class stringTypeError(TypeError):
6 pass
7
8 #节点类
9 class Node(object):
10 def __init__(self, elem, next_ = None):
11 self.elem = elem
12 self.next = next_
13 #单链表类
14 class single_list(object):
15 def __init__(self):
16 self._head = None
17 self._num = 0
18
19 def __len__(self):
20 return self._num
21
22 def prepend(self,elem):
23 self._head = Node(elem, self._head)
24 self._num += 1
25
26 def append(self,elem):
27 if self._head is None:
28 self._head = Node(elem)
29 self._num += 1
30 return
31 p = self._head
32 while p.next:
33 p = p.next
34 p.next = Node(elem)
35 self._num += 1
36
37 def pop_last(self):
38 if self._head is None:
39 raise ValueError("in pop_last")
40 p = self._head
41 if p.next is None:
42 e = p.elem
43 self._head = None
44 self._num -= 1
45 return e
46 while p.next.next:
47 p = p.next
48 e = p.next.elem
49 p.next = None
50 self._num -= 1
51 return e
52
53 def delitem(self, key):
54 if key == len(self)-1:
55 self.pop_last()
56 elif 0<= key < len(self) - 1:
57 p = self._head
58 pre = None
59 num = -1
60 while p is not None:
61 num += 1
62 if key==num:
63 if not pre:
64 self._head = p.next
65 self._num -= 1
66 else:
67 pre.next = p.next
68 self._num -= 1
69 break
70 else:
71 pre = p
72 p = p.next
73 else:
74 raise IndexError
75
76 def insert(self, key, elem):
77 if key>=len(self)-1:
78 self.append(elem)
79 elif 0<=key<len(self)-1:
80 p = self._head
81 pre = None
82 num = -1
83 while p:
84 num += 1
85 if num==key:
86 if not pre:
87 self._head = Node(elem, self._head)
88 self._num += 1
89 else:
90 pre.next = Node(elem, pre.next)
91 self._num += 1
92 break
93 else:
94 pre = p
95 p = p.next
96 else:
97 raise IndexError
98
99 # 打印显示
100 def printall(self):
101 p = self._head
102 while p:
103 print(p.elem, end="")
104 if p.next:
105 print(", ", end="")
106 p = p.next
107 print("")
108
109
110 #单链表字符串类
111 class string(single_list):
112 def __init__(self, value):
113 self.value = str(value)
114 single_list.__init__(self)
115 for i in range(len(self.value)-1,-1,-1):
116 self.prepend(self.value[i])
117
118 def length(self):
119 return self._num
120
121 def printall(self):
122 p = self._head
123 print("字符串结构：",end="")
124 while p:
125 print(p.elem, end="")
126 if p.next:
127 print("-->", end="")
128 p = p.next
129 print("")
130
131 #朴素的串匹配算法，返回匹配的起始位置
132 def naive_matching(self, p): #self为目标字符串，t为要查找的字符串
133 if not isinstance(self, string) and not isinstance(p, string):
134 raise stringTypeError
135 m, n = p.length(), self.length()
136 i, j = 0, 0
137 while i < m and j < n:
138 if p.value[i] == self.value[j]:#字符相同，考虑下一对字符
139 i, j = i+1, j+1
140 else: #字符不同，考虑t中下一个位置
141 i, j = 0, j-i+1
142 if i == m: #i==m说明找到匹配,返回其下标
143 return j-i
144 return -1
145
146 #kmp匹配算法，返回匹配的起始位置
147 def matching_KMP(self, p):
148 j, i = 0, 0
149 n, m = self.length(), p.length()
150 while j < n and i < m:
151 if i == -1 or self.value[j] == p.value[i]:
152 j, i = j + 1, i + 1
153 else:
154 i = string.gen_next(p)[i]
155 if i == m:
156 return j - i
157 return -1
158
159 # 生成pnext表
160 @staticmethod
161 def gen_next(p):
162 i, k, m = 0, -1, p.length()
163 pnext = [-1] * m
164 while i < m - 1:
165 if k == -1 or p.value[i] == p.value[k]:
166 i, k = i + 1, k + 1
167 pnext[i] = k
168 else:
169 k = pnext[k]
170 return pnext
171
172 #把old字符串出现的位置换成new字符串
173 def replace(self, old, new):
174 if not isinstance(self, string) and not isinstance(old, string)
175 and not isinstance(new, string):
176 raise stringTypeError
177
178 #删除匹配的旧字符串
179 start = self.matching_KMP(old)
180 for i in range(old.length()):
181 self.delitem(start)
182 #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
183 if start<self.length():
184 for i in range(new.length()-1, -1, -1):
185 self.insert(start,new.value[i])
186 else:
187 for i in range(new.length()):
188 self.insert(start,new.value[i])
189
190
191 if __name__=="__main__":
192
193 a = string("abcda")
194 print("字符串长度：",a.length())
195 a.printall()
196 b = string("abcabaabcdabdabcda")
197 print("字符串长度：", b.length())
198 b.printall()
199 print("朴素算法_匹配的起始位置：",b.naive_matching(a),end=" ")
200 print("KMP算法_匹配的起始位置：",b.matching_KMP(a))
201 c = string("xu")
202 print("==")
203 b.replace(a,c)
204 print("替换后的字符串是：")
205 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