编程练习 输入一个链表 从尾到头打印节点值
两种方法（改变链表结构或者节点的值）
1，利用栈的方法实现
将节点里的值按顺序push压入到栈中
再将pop出栈的值按顺序赋值到节点里
2.原链表头节点删除 再 头插入到一个新的链表里 实现反转
1 #!/usr/bin/env python3 2 3 class Stack(object): 4 def __init__(self): 5 self._elems = [] 6 7 def is_empty(self): 8 return self._elems == [] 9 10 def push(self, elem): 11 self._elems.append(elem) 12 13 def pop(self): 14 if self.is_empty(): 15 raise ValueError("Stack is Empty") 16 return self._elems.pop() 17 18 def peek(self): 19 if self.is_empty(): 20 raise ValueError("Stack is Empty") 21 return self._elems[-1] 22 23 def bianli(self): 24 return self._elems 25 26 class Node(object): 27 def __init__(self, elem, next_=None): 28 self.elem = elem 29 self.next = next_ 30 31 class Simple_List(object): 32 def __init__(self): 33 self.head = None 34 self.rear = None 35 36 def is_empty(self): 37 return self.head is None 38 39 def prepend(self, elem):
if self.head is None:
40 self.head = Node(elem) 41 self.rear = self.head 42 else: 43 self.head = Node(elem, self.head) 44 45 def prepop(self): 46 if self.head is None: 47 raise ValueError("List is Empty") 48 e = self.head.elem 49 self.head = self.head.next 50 return e 51 52 def append(self, elem): 53 if self.head is None: 54 self.head = Node(elem) 55 self.rear = self.head 56 else: 57 self.rear = Node(elem) 58 self.rear = self.rear.next 59 60 def pop(self): 61 if self.head is None: 62 raise ValueError("List is Empty") 63 p = self.head 64 if p.next is None: 65 self.head = None 66 while p.next.next: 67 p = p.next 68 e = p.next.elem 69 p.next = None 70 self.rear = p 71 return e 72 73 def reverse_stack(self): 74 s1 = Stack() 75 p = self.head 76 while p: 77 s1.push(p.elem) 78 p = p.next 79 p = self.head 80 while p: 81 p.elem = s1.pop() 82 p = p.next 83 84 def reverse(self): 85 li = Simple_List() 86 while not self.is_empty(): 87 li.prepend(self.prepop()) 88 return li 89 90 def bianli(self): 91 p = self.head 92 li = [] 93 while p: 94 li.append(p.elem) 95 p = p.next 96 return li 97 98 if __name__=='__main__': 99 l = Simple_List() 100 for i in range(10): 101 l.prepend(i) 102 print("origin list:",l.bianli()) 103 l.reverse_stack() 104 print("stack reverse:",l.bianli()) 105 print("prepend and prepop reverse:",l.reverse().bianli())
利用栈的方法实现，不改变原链表结构或节点值。只实现节点值的逆序打印。
1 #!/usr/bin/env python3 2 # -*- coding:utf-8 -*- 3 4 class Node(object): 5 def __init__(self, elem, next_=None): 6 self.elem = elem 7 self.next = next_ 8 9 class List(object): 10 def __init__(self): 11 self.head = None 12 13 def is_empty(self): 14 return self.head is None 15 16 def prepend(self, elem): 17 self.head = Node(elem, self.head) 18 19 def prepop(self): 20 if self.is_empty(): 21 raise ValueError("List is Empty") 22 e = self.head.elem 23 self.head = self.head.next 24 return e 25 26 def bianli(self): 27 p = self.head 28 li = [] 29 while p: 30 li.append(p.elem) 31 p = p.next 32 return li 33 34 #栈实现 35 def reverse_print(self): 36 s = Stack() 37 p = self.head 38 li = [] 39 while p: 40 s.push(p.elem) 41 p = p.next 42 while not s.is_empty(): 43 li.append(s.pop()) 44 return li 45 46 class Stack(object): 47 def __init__(self): 48 self.top = None 49 50 def is_empty(self): 51 return self.top is None 52 53 def push(self, elem): 54 self.top = Node(elem, self.top) 55 56 def pop(self): 57 if self.is_empty(): 58 raise ValueError("Stack is Empty") 59 e = self.top.elem 60 self.top = self.top.next 61 return e 62 63 def peek(self): 64 if self.is_empty(): 65 raise ValueError("Stack is Empty") 66 return self.top.elem 67 68 69 if __name__ == '__main__': 70 l = List() 71 for i in range(5): 72 l.prepend(i) 73 print(l.prepop()) 74 print(l.bianli()) 75 print(l.reverse_print())
