def ParseTree(exp):
exp = exp.split()
expTree = BinaryTree('') # create an empty tree
parents = Stack() # create stack to hold the parents
parents.push(expTree) # root is kept on bttm of stack
for item in exp:
if item == '(': # next item will be var or int, followed by an operator - we need to move down
expTree.insertLeft(
''
) # insert empty node on left which will be a num or int later
parents.push(expTree)
expTree = expTree.getLeftChild(
) # move down so num or var can be placed
elif item == ')':
expTree = parents.pop()
elif item in OPERATORS:
expTree.key = item # operator is placed at current node
expTree.insertRight('')
parents.push(expTree)
expTree = expTree.getRightChild(
) # we move right because a symbol or an num must be placed next
elif item not in SYMBOLS and item not in OPERATORS and item != "(" and item != ")":
expTree.key = float(
item
) # entering them as float in case anyone inputs float values
expTree = parents.pop()
elif item in SYMBOLS:
expTree.key = item
expTree = parents.pop()
return expTree
# _*_ coding: utf-8 -*-
# @Time : 8/27/20 3:19 PM
# @Author : title_z
# @Filename : Binarytree.py
from pythonds.trees import BinaryTree
# r = BinaryTree(3)
# BinaryTree.insertLeft(r, 4)
# BinaryTree.insertLeft(r, 5)
# BinaryTree.insertRight(r, 6)
# BinaryTree.insertRight(r, 7)
# l = BinaryTree.getLeftChild(r)
# print(l)
r = BinaryTree('a')
r.insertLeft('b')
r.insertRight('c')
r.getRightChild().setRootVal('hello')
r.getLeftChild().insertRight('d')
print(r)
# 3. Using the findSuccesor method, write a non-recursive inorder traversal for a binary search tree.
from pythonds.basic import Stack
from pythonds.trees import BinaryTree
# Inorder traversal using a Stack
def inorderTrav(tree):
posStack = Stack()
current = tree
while current != None or posStack.size() > 0:
# Left-most node
while (current != None):
posStack.push(current)
current = current.getLeftChild()
current = posStack.pop()
print(current.getRootVal())
current = current.getRightChild()
tree = BinaryTree("A")
tree.insertLeft("B")
tree.getLeftChild().insertLeft("C")
tree.getLeftChild().insertRight("D")
tree.insertRight("E")
inorderTrav(tree)
else:
return tree.getRootVal()
# 还原完全括号表达式
def printExp(tree):
sumVal = ''
if tree:
currentVal = tree.getRootVal()
if isinstance(currentVal, int):
sumVal = printExp(tree.getLeftChild())
else:
sumVal = '(' + printExp(tree.getLeftChild())
sumVal = sumVal + str(tree.getRootVal())
if isinstance(currentVal, int):
sumVal = sumVal + printExp(tree.getRightChild())
else:
sumVal = sumVal + printExp(tree.getRightChild()) + ')'
return sumVal
etree = BinaryTree('*')
etree.insertRight(2)
etree.insertLeft(3)
preorder(etree)
print(printExp(etree))
print(postorderEval(etree))