Problem :
Given a string of opening and closing parentheses,
check whether it’s balanced.
We have 3 types of parentheses: round brackets: (), square brackets:
[], and curly brackets: {}.
Assume that the string doesn’t contain
any other character than these, no spaces words or numbers.
As a reminder, balanced parentheses require every opening
parenthesis to be closed in the reverse order opened.
For example ‘([])’ is balanced but ‘([)]’ is not.
You can assume the input string has no spaces.
Solution :
def check_balanced_string(s1):
if len(s1)%2 != 0:
return False
opening = set('([{')
matches = set([ ('{','}'), ('[',']'), ('(',')') ])
stack = []
for perm in s1:
if perm in opening:
stack.append(perm)
else:
if len(stack) == 0 :
return False
last_val = stack.pop()
if (last_val,perm) not in matches:
return False
return len(stack) == 0
# '([])'
b = check_balanced_string('[()]')
print b
