(Python) Valid Parentheses

Question

Input a string called “s” and if the string is a valid parentheses, output True or else output False.
Could someone help me revise my code as below in the answer zone?

e.g. input ((()())); output True.
Input ((; output False.
I’m very grateful for any helping hand.

Answer 1

https://code.sololearn.com/cOl4mPVX71LJ/?ref=app

Answer 2

Xan
Yeah, that is intuitive, but... If somehow you happen to be using billions of '(', then you may overflow you variable. not that it really matters, but I had to point it out. theoretically, tho, it should loop back again to the positive with the same number, so it should actually work anyways. 🤔
Interesting.

Answer 3

if s.count ("(")==s.count (")") and s.startswith ("(") and s.endswith(")"):
print ("valid")
else:
print ("invalid:)

Answer 4

Manuel Maier
You're talking about a string being as long as you want?
You still need a count variable

Answer 5

https://code.sololearn.com/cJMC3gAAxKYC/#py

Answer 6

I understand the concept more. Thank you guys so much!

Answer 7

def ValidParentheses(s):
s=str(input())
if len(s)%2==0:
c=0
d=0
a=0
b=0
for i in s and k in range(len(s)):
if i==str("(") in s[:k]:
c+=1
if i==str(")") in s[:k]:
d+=1
for i in s:
if i ==str("("):
a+=1
if i==str(")"):
b+=1
if c>=d and a==b:
return True
else:
return False

Answer 8

I think there is a simpler algorithm:

count = 0

if you see an open bracket then count++;
if you see a close bracket then count--

Return true if both these were true:
1) Once processing has finished, count should equal zero
2) Count never went below zero

CASE 1:
(()()(()))
+1 +1 -1 +1 -1 +1 +1 -1 -1 -1
1 2 1 2 1 2 3 2 1 0
[All good]

CASE 2:
))((
-1 -1 +1 +1 = 0
[This ends correctly with 0, meaning same number of open to close brackets, BUT the syntax is wrong]

Completed code:
https://code.sololearn.com/cJMC3gAAxKYC/#py

Answer 9

J.G. In Python the size of an integer is not a problem because they could be as large as the memory in your computer allow it.

Answer 10

Picking up on the theoretical limitations is a pointless debate. To do this properly, we'd build a proper parser. The question is at beginner's level, and therefore so is the answer.

Answer 11

J.G. Also integers have no fixed limit in python. And yes Xan is right, this is not the problem in this task. I think the solution from Pedro Demingos is the best.

Answer 12

Mitali, your code will think this example is valid: "())(()"

That's why the nesting count is needed, see:
https://code.sololearn.com/cJMC3gAAxKYC/#py