def buildParseTree(pexp):
plist = pexp.split()
pStack = Stack()
eTree = BinaryTree('')
pStack.push(eTree)
currentTree = eTree
for i in plist:
if i == '(':
currentTree.insertLeft('')
pStack.push(currentTree)
currentTree = currentTree.getLeftChild()
elif i in ['+', '-', '*', '/']:
currentTree.setRootVal(i)
currentTree.insertRight('')
pStack.push(currentTree)
currentTree = currentTree.getRightChild()
elif i == ')':
currentTree = pStack.pop()
elif i not in ['+', '-', '*', '/', ')']:
try:
currentTree.setRootVal(int(i))
parent = pStack.pop()
currentTree = parent
except ValueError:
raise ValueError(
"token ' {} ' is not a valid integer".format(i))
return eTree
def postfixEval(postfixExpr):
operandstack = Stack()
tokenlist = postfixExpr.split()
for token in tokenlist:
if token in '01234567891011121314151617181920':
operandstack.push(int(token))
else:
operand2 = operandstack.pop()
operand1 = operandstack.pop()
result = doMath(operand1, operand2, token)
operandstack.push(result)
return operandstack.pop()
def divideBy2(decNum):
remstack = Stack()
while decNum > 0:
rem = decNum % 2
remstack.push(rem)
decNum = decNum // 2
binstring = ''
while not remstack.isEmpty():
binstring = binstring + str(remstack.pop())
return binstring
def baseConverter(decNum, base):
digits = "0123456789ABCDEF"
remstack = Stack()
while decNum > 0:
rem = decNum % base
remstack.push(rem)
decNum = decNum // base
binstring = ''
while not remstack.isEmpty():
binstring = binstring + digits[remstack.pop()]
return binstring
def parCheck(symbolstring):
s = Stack()
balanced = True
for index in range(len(symbolstring)):
symbol = symbolstring[index]
if symbol in "([{":
s.push(symbol)
elif symbol in ")]}":
if s.isEmpty() == True:
balanced = False
break
else:
top = s.pop()
if not matches(top, symbol):
balanced = False
break
if balanced and s.isEmpty():
return True
else:
return False
def infixToPostfix(expr):
prec = {'**': 4, '*': 3, '/': 3, '+': 2, '-': 2, '(': 1}
opStack = Stack()
postfixList = []
tokenList = expr.split()
alpha = set(string.ascii_uppercase)
for token in tokenList:
if token in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' or token in '0123456789':
postfixList.append(token)
elif token == '(':
opStack.push(token)
elif token == ')':
toptoken = opStack.pop()
while toptoken != '(':
postfixList.append(toptoken)
toptoken = opStack.pop()
else:
# must put not Stack.isEmpty() first to evaluate if there is a operation token or not
while (not opStack.isEmpty()) and (prec[opStack.peek()] >=
prec[token]):
postfixList.append(opStack.pop())
opStack.push(token)
while not opStack.isEmpty():
postfixList.append(opStack.pop())
return " ".join(postfixList)
return isPalindrome(word[1:-1])
# Convert integer to string of specified base
def toStr(n, base):
convertStr = '0123456789ABCDEF'
if n < base:
return convertStr[n]
else:
return toStr(n // base, base) + convertStr[n % base]
# Convert integer to string of specified base
# using a stack
from BasicDS import Stack
rStack = Stack()
def toStr(n, base):
convertStr = '0123456789ABCDEF'
while n > 0:
if n < base:
rStack.push(convertStr[n])
else:
rStack.push(convertStr[n % base])
n = n // base
res = ""
while not rStack.isEmpty():
res = res + rStack.pop()
return res