def revstring(mystr):
s = Stack()
for c in mystr:
s.push(c)
revstr = ""
while not s.is_empty():
revstr += s.pop()
return revstr
def divide_by_2(dec):
s = Stack()
while dec > 0:
rem = dec % 2
s.push(rem)
dec = dec // 2
bin = ""
while not s.is_empty():
bin += str(s.pop())
return bin
def base_converter(decimal_num, base):
s = Stack()
digits = "0123456789ABCDEF"
while decimal_num > 0:
rem = decimal_num % base
s.push(rem)
decimal_num = decimal_num // base
new_str = ""
while not s.is_empty():
new_str += digits[s.pop()]
return new_str
def par_checker(symbol_string):
s = Stack()
for symbol in symbol_string:
if symbol == "(":
s.push(symbol)
else:
if s.is_empty():
return False
else:
s.pop()
return s.is_empty()
def postfix_eval(postfix_expr):
operand_stack = Stack()
token_list = postfix_expr.split()
for token in token_list:
if token in "0123456789":
operand_stack.push(int(token))
else:
operand2 = operand_stack.pop()
operand1 = operand_stack.pop()
result = do_math(token, operand1, operand2)
operand_stack.push(result)
return operand_stack.pop()
def to_str(n, base):
r_stack = Stack()
convert_string = "0123456789ABCDEF"
while n > 0:
if n < base:
r_stack.push(convert_string[n])
else:
r_stack.push(convert_string[n % base])
n = n // base
res = ""
while not r_stack.is_empty():
res = res + str(r_stack.pop())
return res
def build_parse_tree(fp_expr):
fp_list = fp_expr.split()
p_stack = Stack()
expr_tree = BinaryTree("")
p_stack.push(expr_tree)
current_tree = expr_tree
for i in fp_list:
if i == "(":
current_tree.insert_left("")
p_stack.push(current_tree)
current_tree = current_tree.left_child
elif i in ["+", "-", "*", "/"]:
current_tree.root = i
current_tree.insert_right("")
p_stack.push(current_tree)
current_tree = current_tree.right_child
elif i == ")":
current_tree = p_stack.pop()
elif i not in ["+", "-", "*", "/", ")"]:
try:
current_tree.root = int(i)
parent = p_stack.pop()
current_tree = parent
except ValueError:
raise ValueError("token '{}' is not a valid integer".format(i))
return expr_tree
def infix_to_postfix(infix_expr):
prec = {"^": 4, "*": 3, "/": 3, "+": 2, "-": 2, "(": 1}
op_stack = Stack()
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 == ")":
top_token = op_stack.pop()
while top_token != "(":
postfix_list.append(top_token)
top_token = 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)