def postfix_eval(postfix_expr):
op_stack = ArrayStack()
token_list = postfix_expr.split()
for token in token_list:
if token in "0123456789":
op_stack.push(int(token))
else:
operand2 = op_stack.pop()
operand1 = op_stack.pop()
result = do_math(token, operand1, operand2)
op_stack.push(result)
return op_stack.pop()
def par_checker(symbol_str):
s = ArrayStack()
balanced = True
index = 0
while index < len(symbol_str) and balanced:
symbol = symbol_str[index]
if symbol == "(":
s.push(symbol)
else:
if s.is_empty():
balanced = False
else:
s.pop()
index = index + 1
if balanced and s.is_empty():
return True
else:
return False
def divide_by2(num):
remstack = ArrayStack()
while num > 0:
rem = num % 2
remstack.push(rem)
num = num // 2
bin_str = ""
while not remstack.is_empty():
bin_str = bin_str + str(remstack.pop())
return bin_str
def base_converter(num, base):
digits = "0123456789ABCDEF"
remstack = ArrayStack(max_size=1024)
while num > 0:
rem = num % base
remstack.push(rem)
num = num // base
new_str = ""
while not remstack.is_empty():
new_str = new_str + digits[remstack.pop()]
return new_str
def par_checker2(symbol_str):
s = ArrayStack()
balanced = True
index = 0
while index < len(symbol_str) and balanced:
symbol = symbol_str[index]
if symbol in "([{":
s.push(symbol)
else:
if s.is_empty():
balanced = False
else:
top = s.pop()
if not matches(top, symbol):
balanced = False
index = index + 1
if balanced and s.is_empty():
return True
else:
return False
def test_array_stack():
s = ArrayStack(3)
s.push(1)
s.push(2)
s.push(3)
assert len(s) == 3
with pytest.raises(Exception) as excinfo:
s.push(4)
assert 'full' in str(excinfo)
assert s.pop() == 3
assert not s.is_empty()
assert s.pop() == 2
assert s.pop() == 1
with pytest.raises(Exception) as excinfo:
s.pop()
assert 'empty' in str(excinfo)
assert s.is_empty()
assert len(s) == 0
def infix_to_postfix(infix_expr):
prec = {}
prec["*"] = 3
prec["/"] = 3
prec["+"] = 2
prec["-"] = 2
prec["("] = 1
op_stack = ArrayStack()
postfix_list = []
token_list = infix_expr.split()
for token in token_list:
if token in "ABCDEFGHIJKLMNOPQRSTUVWXYZ" or token in "0123456789":
postfix_list.append(token)
elif token == "(":
op_stack.push(token)
elif token == ")":
topToken = op_stack.pop()
while topToken != "(":
postfix_list.append(topToken)
topToken = op_stack.pop()
else:
while (not op_stack.is_empty()) and (prec[op_stack.peek()] >=
prec[token]):
postfix_list.append(op_stack.pop())
op_stack.push(token)
while not op_stack.is_empty():
postfix_list.append(op_stack.pop())
return " ".join(postfix_list)