Answers:
这是二进制搜索树的简单递归实现。
#!/usr/bin/python
class Node:
def __init__(self, val):
self.l = None
self.r = None
self.v = val
class Tree:
def __init__(self):
self.root = None
def getRoot(self):
return self.root
def add(self, val):
if self.root is None:
self.root = Node(val)
else:
self._add(val, self.root)
def _add(self, val, node):
if val < node.v:
if node.l is not None:
self._add(val, node.l)
else:
node.l = Node(val)
else:
if node.r is not None:
self._add(val, node.r)
else:
node.r = Node(val)
def find(self, val):
if self.root is not None:
return self._find(val, self.root)
else:
return None
def _find(self, val, node):
if val == node.v:
return node
elif (val < node.v and node.l is not None):
self._find(val, node.l)
elif (val > node.v and node.r is not None):
self._find(val, node.r)
def deleteTree(self):
# garbage collector will do this for us.
self.root = None
def printTree(self):
if self.root is not None:
self._printTree(self.root)
def _printTree(self, node):
if node is not None:
self._printTree(node.l)
print(str(node.v) + ' ')
self._printTree(node.r)
# 3
# 0 4
# 2 8
tree = Tree()
tree.add(3)
tree.add(4)
tree.add(0)
tree.add(8)
tree.add(2)
tree.printTree()
print(tree.find(3).v)
print(tree.find(10))
tree.deleteTree()
tree.printTree()
def _find(self, val, node): if(val == node.v): return node elif(val < node.v and node.l != None): return self._find(val, node.l) elif(val > node.v and node.r != None): return self._find(val, node.r)
left<=root<=right
吗?
# simple binary tree
# in this implementation, a node is inserted between an existing node and the root
class BinaryTree():
def __init__(self,rootid):
self.left = None
self.right = None
self.rootid = rootid
def getLeftChild(self):
return self.left
def getRightChild(self):
return self.right
def setNodeValue(self,value):
self.rootid = value
def getNodeValue(self):
return self.rootid
def insertRight(self,newNode):
if self.right == None:
self.right = BinaryTree(newNode)
else:
tree = BinaryTree(newNode)
tree.right = self.right
self.right = tree
def insertLeft(self,newNode):
if self.left == None:
self.left = BinaryTree(newNode)
else:
tree = BinaryTree(newNode)
tree.left = self.left
self.left = tree
def printTree(tree):
if tree != None:
printTree(tree.getLeftChild())
print(tree.getNodeValue())
printTree(tree.getRightChild())
# test tree
def testTree():
myTree = BinaryTree("Maud")
myTree.insertLeft("Bob")
myTree.insertRight("Tony")
myTree.insertRight("Steven")
printTree(myTree)
在此处了解更多信息:-这是一个非常简单的实现二进制树。
这是一个很好的教程,中间有问题
insertLeft
已损坏,并且在尝试递归遍历二叉树最左边的分支时将产生无限循环
[采访所需的内容] Node类是足以表示二叉树的数据结构。
(尽管其他答案大多数都是正确的,但对于二叉树而言,它们不是必需的:无需扩展对象类,无需成为BST,无需导入双端队列)。
class Node:
def __init__(self, value = None):
self.left = None
self.right = None
self.value = value
这是一棵树的例子:
n1 = Node(1)
n2 = Node(2)
n3 = Node(3)
n1.left = n2
n1.right = n3
在此示例中,n1是具有n2,n3作为其子级的树的根。
BST在Python中的简单实现
class TreeNode:
def __init__(self, value):
self.left = None
self.right = None
self.data = value
class Tree:
def __init__(self):
self.root = None
def addNode(self, node, value):
if(node==None):
self.root = TreeNode(value)
else:
if(value<node.data):
if(node.left==None):
node.left = TreeNode(value)
else:
self.addNode(node.left, value)
else:
if(node.right==None):
node.right = TreeNode(value)
else:
self.addNode(node.right, value)
def printInorder(self, node):
if(node!=None):
self.printInorder(node.left)
print(node.data)
self.printInorder(node.right)
def main():
testTree = Tree()
testTree.addNode(testTree.root, 200)
testTree.addNode(testTree.root, 300)
testTree.addNode(testTree.root, 100)
testTree.addNode(testTree.root, 30)
testTree.printInorder(testTree.root)
使用列表实现二叉树的一种非常快捷的方法。这不是最有效的方法,也不能很好地处理nil值。但这非常透明(至少对我而言):
def _add(node, v):
new = [v, [], []]
if node:
left, right = node[1:]
if not left:
left.extend(new)
elif not right:
right.extend(new)
else:
_add(left, v)
else:
node.extend(new)
def binary_tree(s):
root = []
for e in s:
_add(root, e)
return root
def traverse(n, order):
if n:
v = n[0]
if order == 'pre':
yield v
for left in traverse(n[1], order):
yield left
if order == 'in':
yield v
for right in traverse(n[2], order):
yield right
if order == 'post':
yield v
从可迭代构造树:
>>> tree = binary_tree('A B C D E'.split())
>>> print tree
['A', ['B', ['D', [], []], ['E', [], []]], ['C', [], []]]
遍历一棵树:
>>> list(traverse(tree, 'pre')), list(traverse(tree, 'in')), list(traverse(tree, 'post'))
(['A', 'B', 'D', 'E', 'C'],
['D', 'B', 'E', 'A', 'C'],
['D', 'E', 'B', 'C', 'A'])
我不禁注意到这里的大多数答案都在实现二进制搜索树。二进制搜索树!=二进制树。
二叉搜索树具有非常特殊的属性:对于任何节点X,X的密钥都大于其左子节点的任何后代的关键字,并且小于其右子节点的任何后代的关键字。
二叉树不施加这样的限制。二叉树只是具有“键”元素和两个孩子的数据结构,分别是“左”和“右”。
树是二进制树的更一般的情况,其中每个节点可以具有任意数量的子代。通常,每个节点都有一个“孩子”元素,其类型为列表/数组。
现在,为了回答OP的问题,我将在Python中包含Binary Tree的完整实现。给定它提供最佳的O(1)查找,存储每个BinaryTreeNode的基础数据结构是一个字典。我还实现了深度优先遍历和深度优先遍历。这些是在树上执行的非常常见的操作。
from collections import deque
class BinaryTreeNode:
def __init__(self, key, left=None, right=None):
self.key = key
self.left = left
self.right = right
def __repr__(self):
return "%s l: (%s) r: (%s)" % (self.key, self.left, self.right)
def __eq__(self, other):
if self.key == other.key and \
self.right == other.right and \
self.left == other.left:
return True
else:
return False
class BinaryTree:
def __init__(self, root_key=None):
# maps from BinaryTreeNode key to BinaryTreeNode instance.
# Thus, BinaryTreeNode keys must be unique.
self.nodes = {}
if root_key is not None:
# create a root BinaryTreeNode
self.root = BinaryTreeNode(root_key)
self.nodes[root_key] = self.root
def add(self, key, left_key=None, right_key=None):
if key not in self.nodes:
# BinaryTreeNode with given key does not exist, create it
self.nodes[key] = BinaryTreeNode(key)
# invariant: self.nodes[key] exists
# handle left child
if left_key is None:
self.nodes[key].left = None
else:
if left_key not in self.nodes:
self.nodes[left_key] = BinaryTreeNode(left_key)
# invariant: self.nodes[left_key] exists
self.nodes[key].left = self.nodes[left_key]
# handle right child
if right_key == None:
self.nodes[key].right = None
else:
if right_key not in self.nodes:
self.nodes[right_key] = BinaryTreeNode(right_key)
# invariant: self.nodes[right_key] exists
self.nodes[key].right = self.nodes[right_key]
def remove(self, key):
if key not in self.nodes:
raise ValueError('%s not in tree' % key)
# remove key from the list of nodes
del self.nodes[key]
# if node removed is left/right child, update parent node
for k in self.nodes:
if self.nodes[k].left and self.nodes[k].left.key == key:
self.nodes[k].left = None
if self.nodes[k].right and self.nodes[k].right.key == key:
self.nodes[k].right = None
return True
def _height(self, node):
if node is None:
return 0
else:
return 1 + max(self._height(node.left), self._height(node.right))
def height(self):
return self._height(self.root)
def size(self):
return len(self.nodes)
def __repr__(self):
return str(self.traverse_inorder(self.root))
def bfs(self, node):
if not node or node not in self.nodes:
return
reachable = []
q = deque()
# add starting node to queue
q.append(node)
while len(q):
visit = q.popleft()
# add currently visited BinaryTreeNode to list
reachable.append(visit)
# add left/right children as needed
if visit.left:
q.append(visit.left)
if visit.right:
q.append(visit.right)
return reachable
# visit left child, root, then right child
def traverse_inorder(self, node, reachable=None):
if not node or node.key not in self.nodes:
return
if reachable is None:
reachable = []
self.traverse_inorder(node.left, reachable)
reachable.append(node.key)
self.traverse_inorder(node.right, reachable)
return reachable
# visit left and right children, then root
# root of tree is always last to be visited
def traverse_postorder(self, node, reachable=None):
if not node or node.key not in self.nodes:
return
if reachable is None:
reachable = []
self.traverse_postorder(node.left, reachable)
self.traverse_postorder(node.right, reachable)
reachable.append(node.key)
return reachable
# visit root, left, then right children
# root is always visited first
def traverse_preorder(self, node, reachable=None):
if not node or node.key not in self.nodes:
return
if reachable is None:
reachable = []
reachable.append(node.key)
self.traverse_preorder(node.left, reachable)
self.traverse_preorder(node.right, reachable)
return reachable
你不需要两节课
class Tree:
val = None
left = None
right = None
def __init__(self, val):
self.val = val
def insert(self, val):
if self.val is not None:
if val < self.val:
if self.left is not None:
self.left.insert(val)
else:
self.left = Tree(val)
elif val > self.val:
if self.right is not None:
self.right.insert(val)
else:
self.right = Tree(val)
else:
return
else:
self.val = val
print("new node added")
def showTree(self):
if self.left is not None:
self.left.showTree()
print(self.val, end = ' ')
if self.right is not None:
self.right.showTree()
多一点“ Pythonic”?
class Node:
def __init__(self, value):
self.value = value
self.left = None
self.right = None
def __repr__(self):
return str(self.value)
class BST:
def __init__(self):
self.root = None
def __repr__(self):
self.sorted = []
self.get_inorder(self.root)
return str(self.sorted)
def get_inorder(self, node):
if node:
self.get_inorder(node.left)
self.sorted.append(str(node.value))
self.get_inorder(node.right)
def add(self, value):
if not self.root:
self.root = Node(value)
else:
self._add(self.root, value)
def _add(self, node, value):
if value <= node.value:
if node.left:
self._add(node.left, value)
else:
node.left = Node(value)
else:
if node.right:
self._add(node.right, value)
else:
node.right = Node(value)
from random import randint
bst = BST()
for i in range(100):
bst.add(randint(1, 1000))
print (bst)
#!/usr/bin/python
class BinaryTree:
def __init__(self, left, right, data):
self.left = left
self.right = right
self.data = data
def pre_order_traversal(root):
print(root.data, end=' ')
if root.left != None:
pre_order_traversal(root.left)
if root.right != None:
pre_order_traversal(root.right)
def in_order_traversal(root):
if root.left != None:
in_order_traversal(root.left)
print(root.data, end=' ')
if root.right != None:
in_order_traversal(root.right)
def post_order_traversal(root):
if root.left != None:
post_order_traversal(root.left)
if root.right != None:
post_order_traversal(root.right)
print(root.data, end=' ')
一个 Node
基类连接的节点的是一个标准的做法。这些可能很难想象。
摘自有关Python模式-实现图形的文章,请考虑一个简单的字典:
给定
二叉树
a
/ \
b c
/ \ \
d e f
码
制作一个唯一节点的字典:
tree = {
"a": ["b", "c"],
"b": ["d", "e"],
"c": [None, "f"],
"d": [None, None],
"e": [None, None],
"f": [None, None],
}
细节
find_all_paths()
)。基于树的功能通常包括以下常见操作:
尝试实施所有这些操作。在这里,我们演示这些功能之一 -BFS遍历:
例
import collections as ct
def traverse(tree):
"""Yield nodes from a tree via BFS."""
q = ct.deque() # 1
root = next(iter(tree)) # 2
q.append(root)
while q:
node = q.popleft()
children = filter(None, tree.get(node))
for n in children: # 3
q.append(n)
yield node
list(traverse(tree))
# ['a', 'b', 'c', 'd', 'e', 'f']
这是应用于节点和子级字典的广度优先搜索(级别顺序)算法。
deque
,但使用queue
或list
作品(后者效率低下)。另请参阅此有关树的深入教程。
洞察力
一般而言,遍历有很多好处,我们只需将队列替换为堆栈即可轻松地将后者的迭代方法更改为深度优先搜索(DFS)(即LIFO队列))。这仅表示我们从排队的同一侧出队。DFS允许我们搜索每个分支。
怎么样?由于我们使用deque
,我们可以通过更改node = q.popleft()
为node = q.pop()
(右)来模拟堆栈。结果是正确的,预购的DFS:['a', 'c', 'f', 'b', 'e', 'd']
。
import random
class TreeNode:
def __init__(self, key):
self.key = key
self.left = None
self.right = None
self.p = None
class BinaryTree:
def __init__(self):
self.root = None
def length(self):
return self.size
def inorder(self, node):
if node == None:
return None
else:
self.inorder(node.left)
print node.key,
self.inorder(node.right)
def search(self, k):
node = self.root
while node != None:
if node.key == k:
return node
if node.key > k:
node = node.left
else:
node = node.right
return None
def minimum(self, node):
x = None
while node.left != None:
x = node.left
node = node.left
return x
def maximum(self, node):
x = None
while node.right != None:
x = node.right
node = node.right
return x
def successor(self, node):
parent = None
if node.right != None:
return self.minimum(node.right)
parent = node.p
while parent != None and node == parent.right:
node = parent
parent = parent.p
return parent
def predecessor(self, node):
parent = None
if node.left != None:
return self.maximum(node.left)
parent = node.p
while parent != None and node == parent.left:
node = parent
parent = parent.p
return parent
def insert(self, k):
t = TreeNode(k)
parent = None
node = self.root
while node != None:
parent = node
if node.key > t.key:
node = node.left
else:
node = node.right
t.p = parent
if parent == None:
self.root = t
elif t.key < parent.key:
parent.left = t
else:
parent.right = t
return t
def delete(self, node):
if node.left == None:
self.transplant(node, node.right)
elif node.right == None:
self.transplant(node, node.left)
else:
succ = self.minimum(node.right)
if succ.p != node:
self.transplant(succ, succ.right)
succ.right = node.right
succ.right.p = succ
self.transplant(node, succ)
succ.left = node.left
succ.left.p = succ
def transplant(self, node, newnode):
if node.p == None:
self.root = newnode
elif node == node.p.left:
node.p.left = newnode
else:
node.p.right = newnode
if newnode != None:
newnode.p = node.p
此实现支持插入,查找和删除操作,而不会破坏树的结构。这不是平衡树。
# Class for construct the nodes of the tree. (Subtrees)
class Node:
def __init__(self, key, parent_node = None):
self.left = None
self.right = None
self.key = key
if parent_node == None:
self.parent = self
else:
self.parent = parent_node
# Class with the structure of the tree.
# This Tree is not balanced.
class Tree:
def __init__(self):
self.root = None
# Insert a single element
def insert(self, x):
if(self.root == None):
self.root = Node(x)
else:
self._insert(x, self.root)
def _insert(self, x, node):
if(x < node.key):
if(node.left == None):
node.left = Node(x, node)
else:
self._insert(x, node.left)
else:
if(node.right == None):
node.right = Node(x, node)
else:
self._insert(x, node.right)
# Given a element, return a node in the tree with key x.
def find(self, x):
if(self.root == None):
return None
else:
return self._find(x, self.root)
def _find(self, x, node):
if(x == node.key):
return node
elif(x < node.key):
if(node.left == None):
return None
else:
return self._find(x, node.left)
elif(x > node.key):
if(node.right == None):
return None
else:
return self._find(x, node.right)
# Given a node, return the node in the tree with the next largest element.
def next(self, node):
if node.right != None:
return self._left_descendant(node.right)
else:
return self._right_ancestor(node)
def _left_descendant(self, node):
if node.left == None:
return node
else:
return self._left_descendant(node.left)
def _right_ancestor(self, node):
if node.key <= node.parent.key:
return node.parent
else:
return self._right_ancestor(node.parent)
# Delete an element of the tree
def delete(self, x):
node = self.find(x)
if node == None:
print(x, "isn't in the tree")
else:
if node.right == None:
if node.left == None:
if node.key < node.parent.key:
node.parent.left = None
del node # Clean garbage
else:
node.parent.right = None
del Node # Clean garbage
else:
node.key = node.left.key
node.left = None
else:
x = self.next(node)
node.key = x.key
x = None
# tests
t = Tree()
t.insert(5)
t.insert(8)
t.insert(3)
t.insert(4)
t.insert(6)
t.insert(2)
t.delete(8)
t.delete(5)
t.insert(9)
t.insert(1)
t.delete(2)
t.delete(100)
# Remember: Find method return the node object.
# To return a number use t.find(nº).key
# But it will cause an error if the number is not in the tree.
print(t.find(5))
print(t.find(8))
print(t.find(4))
print(t.find(6))
print(t.find(9))
我知道已经发布了许多好的解决方案,但是对于二叉树,我通常采用不同的方法:使用某些Node类并直接实现它更具可读性,但是当您有很多节点时,对于内存可能会变得非常贪婪,所以我建议增加一层复杂性并将节点存储在python列表中,然后仅使用该列表来模拟树的行为。
您仍然可以定义Node类,以在需要时最终表示树中的节点,但是将它们以简单的形式[value,left,right]保留在列表中将使用一半的内存或更少的内存!
这是二进制搜索树类的快速示例,该类将节点存储在数组中。它提供了基本功能,例如添加,删除,查找...
"""
Basic Binary Search Tree class without recursion...
"""
__author__ = "@fbparis"
class Node(object):
__slots__ = "value", "parent", "left", "right"
def __init__(self, value, parent=None, left=None, right=None):
self.value = value
self.parent = parent
self.left = left
self.right = right
def __repr__(self):
return "<%s object at %s: parent=%s, left=%s, right=%s, value=%s>" % (self.__class__.__name__, hex(id(self)), self.parent, self.left, self.right, self.value)
class BinarySearchTree(object):
__slots__ = "_tree"
def __init__(self, *args):
self._tree = []
if args:
for x in args[0]:
self.add(x)
def __len__(self):
return len(self._tree)
def __repr__(self):
return "<%s object at %s with %d nodes>" % (self.__class__.__name__, hex(id(self)), len(self))
def __str__(self, nodes=None, level=0):
ret = ""
if nodes is None:
if len(self):
nodes = [0]
else:
nodes = []
for node in nodes:
if node is None:
continue
ret += "-" * level + " %s\n" % self._tree[node][0]
ret += self.__str__(self._tree[node][2:4], level + 1)
if level == 0:
ret = ret.strip()
return ret
def __contains__(self, value):
if len(self):
node_index = 0
while self._tree[node_index][0] != value:
if value < self._tree[node_index][0]:
node_index = self._tree[node_index][2]
else:
node_index = self._tree[node_index][3]
if node_index is None:
return False
return True
return False
def __eq__(self, other):
return self._tree == other._tree
def add(self, value):
if len(self):
node_index = 0
while self._tree[node_index][0] != value:
if value < self._tree[node_index][0]:
b = self._tree[node_index][2]
k = 2
else:
b = self._tree[node_index][3]
k = 3
if b is None:
self._tree[node_index][k] = len(self)
self._tree.append([value, node_index, None, None])
break
node_index = b
else:
self._tree.append([value, None, None, None])
def remove(self, value):
if len(self):
node_index = 0
while self._tree[node_index][0] != value:
if value < self._tree[node_index][0]:
node_index = self._tree[node_index][2]
else:
node_index = self._tree[node_index][3]
if node_index is None:
raise KeyError
if self._tree[node_index][2] is not None:
b, d = 2, 3
elif self._tree[node_index][3] is not None:
b, d = 3, 2
else:
i = node_index
b = None
if b is not None:
i = self._tree[node_index][b]
while self._tree[i][d] is not None:
i = self._tree[i][d]
p = self._tree[i][1]
b = self._tree[i][b]
if p == node_index:
self._tree[p][5-d] = b
else:
self._tree[p][d] = b
if b is not None:
self._tree[b][1] = p
self._tree[node_index][0] = self._tree[i][0]
else:
p = self._tree[i][1]
if p is not None:
if self._tree[p][2] == i:
self._tree[p][2] = None
else:
self._tree[p][3] = None
last = self._tree.pop()
n = len(self)
if i < n:
self._tree[i] = last[:]
if last[2] is not None:
self._tree[last[2]][1] = i
if last[3] is not None:
self._tree[last[3]][1] = i
if self._tree[last[1]][2] == n:
self._tree[last[1]][2] = i
else:
self._tree[last[1]][3] = i
else:
raise KeyError
def find(self, value):
if len(self):
node_index = 0
while self._tree[node_index][0] != value:
if value < self._tree[node_index][0]:
node_index = self._tree[node_index][2]
else:
node_index = self._tree[node_index][3]
if node_index is None:
return None
return Node(*self._tree[node_index])
return None
我添加了一个父属性,以便您可以删除任何节点并维护BST结构。
抱歉,为了便于阅读,尤其是对于“删除”功能。基本上,当一个节点被删除时,我们弹出树数组并用最后一个元素替换它(除非我们想删除最后一个节点)。为了维持BST结构,将删除的节点替换为其左侧子节点的最大值或右侧子节点的最小值,并且必须执行一些操作才能使索引有效,但它必须足够快。
我将这种技术用于更高级的东西,用内部基数trie构建了一些大单词字典,并且我能够将内存消耗除以7-8(您可以在此处看到示例:https : //gist.github.com/fbparis / b3ddd5673b603b42c880974b23db7cda)
二进制搜索树的良好实现,取自此处:
'''
A binary search Tree
'''
from __future__ import print_function
class Node:
def __init__(self, label, parent):
self.label = label
self.left = None
self.right = None
#Added in order to delete a node easier
self.parent = parent
def getLabel(self):
return self.label
def setLabel(self, label):
self.label = label
def getLeft(self):
return self.left
def setLeft(self, left):
self.left = left
def getRight(self):
return self.right
def setRight(self, right):
self.right = right
def getParent(self):
return self.parent
def setParent(self, parent):
self.parent = parent
class BinarySearchTree:
def __init__(self):
self.root = None
def insert(self, label):
# Create a new Node
new_node = Node(label, None)
# If Tree is empty
if self.empty():
self.root = new_node
else:
#If Tree is not empty
curr_node = self.root
#While we don't get to a leaf
while curr_node is not None:
#We keep reference of the parent node
parent_node = curr_node
#If node label is less than current node
if new_node.getLabel() < curr_node.getLabel():
#We go left
curr_node = curr_node.getLeft()
else:
#Else we go right
curr_node = curr_node.getRight()
#We insert the new node in a leaf
if new_node.getLabel() < parent_node.getLabel():
parent_node.setLeft(new_node)
else:
parent_node.setRight(new_node)
#Set parent to the new node
new_node.setParent(parent_node)
def delete(self, label):
if (not self.empty()):
#Look for the node with that label
node = self.getNode(label)
#If the node exists
if(node is not None):
#If it has no children
if(node.getLeft() is None and node.getRight() is None):
self.__reassignNodes(node, None)
node = None
#Has only right children
elif(node.getLeft() is None and node.getRight() is not None):
self.__reassignNodes(node, node.getRight())
#Has only left children
elif(node.getLeft() is not None and node.getRight() is None):
self.__reassignNodes(node, node.getLeft())
#Has two children
else:
#Gets the max value of the left branch
tmpNode = self.getMax(node.getLeft())
#Deletes the tmpNode
self.delete(tmpNode.getLabel())
#Assigns the value to the node to delete and keesp tree structure
node.setLabel(tmpNode.getLabel())
def getNode(self, label):
curr_node = None
#If the tree is not empty
if(not self.empty()):
#Get tree root
curr_node = self.getRoot()
#While we don't find the node we look for
#I am using lazy evaluation here to avoid NoneType Attribute error
while curr_node is not None and curr_node.getLabel() is not label:
#If node label is less than current node
if label < curr_node.getLabel():
#We go left
curr_node = curr_node.getLeft()
else:
#Else we go right
curr_node = curr_node.getRight()
return curr_node
def getMax(self, root = None):
if(root is not None):
curr_node = root
else:
#We go deep on the right branch
curr_node = self.getRoot()
if(not self.empty()):
while(curr_node.getRight() is not None):
curr_node = curr_node.getRight()
return curr_node
def getMin(self, root = None):
if(root is not None):
curr_node = root
else:
#We go deep on the left branch
curr_node = self.getRoot()
if(not self.empty()):
curr_node = self.getRoot()
while(curr_node.getLeft() is not None):
curr_node = curr_node.getLeft()
return curr_node
def empty(self):
if self.root is None:
return True
return False
def __InOrderTraversal(self, curr_node):
nodeList = []
if curr_node is not None:
nodeList.insert(0, curr_node)
nodeList = nodeList + self.__InOrderTraversal(curr_node.getLeft())
nodeList = nodeList + self.__InOrderTraversal(curr_node.getRight())
return nodeList
def getRoot(self):
return self.root
def __isRightChildren(self, node):
if(node == node.getParent().getRight()):
return True
return False
def __reassignNodes(self, node, newChildren):
if(newChildren is not None):
newChildren.setParent(node.getParent())
if(node.getParent() is not None):
#If it is the Right Children
if(self.__isRightChildren(node)):
node.getParent().setRight(newChildren)
else:
#Else it is the left children
node.getParent().setLeft(newChildren)
#This function traversal the tree. By default it returns an
#In order traversal list. You can pass a function to traversal
#The tree as needed by client code
def traversalTree(self, traversalFunction = None, root = None):
if(traversalFunction is None):
#Returns a list of nodes in preOrder by default
return self.__InOrderTraversal(self.root)
else:
#Returns a list of nodes in the order that the users wants to
return traversalFunction(self.root)
#Returns an string of all the nodes labels in the list
#In Order Traversal
def __str__(self):
list = self.__InOrderTraversal(self.root)
str = ""
for x in list:
str = str + " " + x.getLabel().__str__()
return str
def InPreOrder(curr_node):
nodeList = []
if curr_node is not None:
nodeList = nodeList + InPreOrder(curr_node.getLeft())
nodeList.insert(0, curr_node.getLabel())
nodeList = nodeList + InPreOrder(curr_node.getRight())
return nodeList
def testBinarySearchTree():
r'''
Example
8
/ \
3 10
/ \ \
1 6 14
/ \ /
4 7 13
'''
r'''
Example After Deletion
7
/ \
1 4
'''
t = BinarySearchTree()
t.insert(8)
t.insert(3)
t.insert(6)
t.insert(1)
t.insert(10)
t.insert(14)
t.insert(13)
t.insert(4)
t.insert(7)
#Prints all the elements of the list in order traversal
print(t.__str__())
if(t.getNode(6) is not None):
print("The label 6 exists")
else:
print("The label 6 doesn't exist")
if(t.getNode(-1) is not None):
print("The label -1 exists")
else:
print("The label -1 doesn't exist")
if(not t.empty()):
print(("Max Value: ", t.getMax().getLabel()))
print(("Min Value: ", t.getMin().getLabel()))
t.delete(13)
t.delete(10)
t.delete(8)
t.delete(3)
t.delete(6)
t.delete(14)
#Gets all the elements of the tree In pre order
#And it prints them
list = t.traversalTree(InPreOrder, t.root)
for x in list:
print(x)
if __name__ == "__main__":
testBinarySearchTree()
我想展示@apadana方法的一种变体,当有大量节点时,它会更有用:
'''
Suppose we have the following tree
10
/ \
11 9
/ \ / \
7 12 15 8
'''
# Step 1 - Create nodes - Use a list instead of defining each node separately
nlist = [10,11,7,9,15,8,12]; n = []
for i in range(len(nlist)): n.append(Node(nlist[i]))
# Step 2 - Set each node position
n[0].left = n[1]
n[1].left = n[2]
n[0].right = n[3]
n[3].left = n[4]
n[3].right = n[5]
n[1].right = n[6]
class Node:
"""
single Node for tree
"""
def __init__(self, data):
self.data = data
self.right = None
self.left = None
class binaryTree:
"""
binary tree implementation
"""
def __init__(self):
self.root = None
def push(self, element, node=None):
if node is None:
node = self.root
if self.root is None:
self.root = Node(element)
else:
if element < node.data:
if node.left is not None:
self.push(element, node.left)
else:
node.left = Node(element)
else:
if node.right is not None:
self.push(element, node.right)
else:
node.right = Node(element)
def __str__(self):
self.printInorder(self.root)
return "\n"
def printInorder(self, node):
"""
print tree in inorder
"""
if node is not None:
self.printInorder(node.left)
print(node.data)
self.printInorder(node.right)
def main():
"""
Main code and logic comes here
"""
tree = binaryTree()
tree.push(5)
tree.push(3)
tree.push(1)
tree.push(3)
tree.push(0)
tree.push(2)
tree.push(9)
tree.push(10)
print(tree)
if __name__ == "__main__":
main()
Python中的二叉树
class Tree(object):
def __init__(self):
self.data=None
self.left=None
self.right=None
def insert(self, x, root):
if root==None:
t=node(x)
t.data=x
t.right=None
t.left=None
root=t
return root
elif x<root.data:
root.left=self.insert(x, root.left)
else:
root.right=self.insert(x, root.right)
return root
def printTree(self, t):
if t==None:
return
self.printTree(t.left)
print t.data
self.printTree(t.right)
class node(object):
def __init__(self, x):
self.x=x
bt=Tree()
root=None
n=int(raw_input())
a=[]
for i in range(n):
a.append(int(raw_input()))
for i in range(n):
root=bt.insert(a[i], root)
bt.printTree(root)
这是一个简单的解决方案,可以使用递归方法来构建二叉树,以在下面的代码中使用遍历顺序来显示树。
class Node(object):
def __init__(self):
self.left = None
self.right = None
self.value = None
@property
def get_value(self):
return self.value
@property
def get_left(self):
return self.left
@property
def get_right(self):
return self.right
@get_left.setter
def set_left(self, left_node):
self.left = left_node
@get_value.setter
def set_value(self, value):
self.value = value
@get_right.setter
def set_right(self, right_node):
self.right = right_node
def create_tree(self):
_node = Node() #creating new node.
_x = input("Enter the node data(-1 for null)")
if(_x == str(-1)): #for defining no child.
return None
_node.set_value = _x #setting the value of the node.
print("Enter the left child of {}".format(_x))
_node.set_left = self.create_tree() #setting the left subtree
print("Enter the right child of {}".format(_x))
_node.set_right = self.create_tree() #setting the right subtree.
return _node
def pre_order(self, root):
if root is not None:
print(root.get_value)
self.pre_order(root.get_left)
self.pre_order(root.get_right)
if __name__ == '__main__':
node = Node()
root_node = node.create_tree()
node.pre_order(root_node)
代码取自:Python中的二叉树