数据结构：单链表结构字符串（python版）

 #!/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