二叉树的实现(补充)

Posted 2022-08-24 yang-he

二叉树的实现(补充)

本次实现的二叉树包括二叉树的先序遍历，中序遍历和后序遍历以及二叉树的层序遍历，还包括二叉树的高度，叶子节点以及反转二叉树

二叉树的层序遍历依然是使用Python内置的deque实现一个队列，根据队列先进先出(FIFO)的性质，先把二叉树的根节点放入队列中，判断队列是否为空，如果不为空，则弹出一个元素，打印该元素的值，如果该元素有左孩子，则把左孩子入队，如果有右孩子，则把有孩子入队

代码:

  1 from collections import deque
  2 
  3 
  4 class Queue:  # 借助内置的 deque 我们可以迅速实现一个 Queue
  5     def __init__(self):
  6         self._elem = deque()
  7 
  8     def append(self, value):
  9         return self._elem.append(value)
 10 
 11     def pop(self):
 12         return self._elem.popleft()
 13 
 14     def empty(self):
 15         return len(self._elem) == 0
 16 
 17 
 18 class BTree(object):
 19     def __init__(self, data=None, left=None, right=None):
 20         self.data = data
 21         self.left = left
 22         self.right = right
 23 
 24     def preorder(self):
 25         if self.data is not None:
 26             print(self.data, end=‘,‘)
 27         if self.left is not None:
 28             self.left.preorder()
 29         if self.right is not None:
 30             self.right.preorder()
 31 
 32     def midorder(self):
 33         if self.left is not None:
 34             self.left.midorder()
 35         if self.data is not None:
 36             print(self.data, end=‘,‘)
 37         if self.right is not None:
 38             self.right.midorder()
 39 
 40     def postorder(self):
 41         if self.left is not None:
 42             self.left.postorder()
 43         if self.right is not None:
 44             self.right.postorder()
 45         if self.data is not None:
 46             print(self.data, end=‘,‘)
 47 
 48     def levelorder(self):
 49 
 50         # 返回某个节点的左孩子
 51         def LChild_Of_Node(node):
 52             return node.left if node.left is not None else None
 53 
 54         # 返回某个节点的右孩子
 55         def RChild_Of_Node(node):
 56             return node.right if node.right is not None else None
 57 
 58         # 层序遍历列表
 59         level_order = []
 60         # 是否添加根节点中的数据
 61         if self.data is not None:
 62             level_order.append([self])
 63 
 64         # 二叉树的高度
 65         height = self.height()
 66         if height >= 1:
 67             # 对第二层及其以后的层数进行操作, 在level_order中添加节点而不是数据
 68             for _ in range(2, height + 1):
 69                 level = []  # 该层的节点
 70                 for node in level_order[-1]:
 71                     # 如果左孩子非空，则添加左孩子
 72                     if LChild_Of_Node(node):
 73                         level.append(LChild_Of_Node(node))
 74                     # 如果右孩子非空，则添加右孩子
 75                     if RChild_Of_Node(node):
 76                         level.append(RChild_Of_Node(node))
 77                 # 如果该层非空，则添加该层
 78                 if level:
 79                     level_order.append(level)
 80 
 81             # 取出每层中的数据
 82             for i in range(0, height):  # 层数
 83                 for index in range(len(level_order[i])):
 84                     level_order[i][index] = level_order[i][index].data
 85 
 86         return level_order
 87 
 88     def height(self):
 89         if self.data is None:
 90             return 0
 91         elif self.left is None and self.right is None:
 92             return 1
 93         elif self.left is None and self.right is not None:
 94             return 1 + self.left.height()
 95         elif self.left is not None and self.right is None:
 96             return 1 + self.left.height()
 97         else:
 98             return 1 + max(self.left.height(), self.right.height())
 99 
100     def leaves(self):
101         if self.data is None:
102             return None
103         elif self.left is None and self.right is None:
104             print(self.data, end=‘,‘)
105         elif self.left is None and self.right is not None:
106             self.right.leaves()
107         elif self.left is not None and self.right is None:
108             self.left.leaves()
109         else:
110             self.left.leaves()
111             self.right.leaves()
112 
113     # 反转二叉树
114     def reverse(self):
115         if self.data is not None:
116             if self.left and self.right:
117                 self.left, self.right = self.right, self.left
118                 self.left.reverse()
119                 self.right.reverse()
120 
121     # @staticmethod
122     # def layer_trav(subtree):
123     #     cur_nodes = [subtree]  # current layer nodes
124     #     next_nodes = []
125     #     while cur_nodes or next_nodes:
126     #         for node in cur_nodes:
127     #             print(node.data, end=‘,‘)
128     #             if node.left:
129     #                 next_nodes.append(node.left)
130     #             if node.right:
131     #                 next_nodes.append(node.right)
132     #         cur_nodes = next_nodes  # 继续遍历下一层
133     #         next_nodes = []
134 
135     @staticmethod
136     def layer_trav(subtree):
137         q = Queue()
138         q.append(subtree)
139         while not q.empty():
140             node = q.pop()
141             print(node.data, end=‘,‘)
142             if node.left:
143                 q.append(node.left)
144             if node.right:
145                 q.append(node.right)
146 
147 
148 if __name__ == ‘__main__‘:
149     right_tree = BTree(6)
150     right_tree.left = BTree(2)
151     right_tree.right = BTree(4)
152 
153     left_tree = BTree(5)
154     left_tree.left = BTree(1)
155     left_tree.right = BTree(3)
156 
157     tree = BTree(11)
158     tree.left = left_tree
159     tree.right = right_tree
160 
161     left_tree = BTree(7)
162     left_tree.left = BTree(3)
163     left_tree.right = BTree(4)
164 
165     right_tree = tree  # 增加新的变量
166     tree = BTree(18)
167     tree.left = left_tree
168     tree.right = right_tree
169     tree.root = tree
170 
171     print(‘先序遍历为:‘)
172     tree.preorder()
173     print(‘\n‘)
174 
175     print(‘后序遍历为:‘)
176     tree.postorder()
177     print(‘\n‘)
178 
179     print(‘中序遍历为:‘)
180     tree.midorder()
181     print(‘\n‘)
182 
183     print(‘层序遍历为:‘)
184     level_order = tree.levelorder()
185     tree.layer_trav(tree)
186     print(‘\n‘)
187     print(level_order)
188 
189     print(‘叶子节点为:‘)
190     tree.leaves()
191     print(‘\n‘)
192 
193     print(‘树的高度为:‘)
194     print(tree.height())
195     print(‘\n‘)
196 
197     print(‘反转二叉树‘)
198     tree.reverse()
199     print(‘先序遍历‘)
200     tree.preorder()
201     print(‘\n‘)
202     print(‘层序遍历‘)
203     tree.layer_trav(tree)