#https://leetcode.com/problems/valid-parentheses/

class Solution(object):

def isValid(self, s):

if (s==''):

return True

elif ('()' in s):

return self.isValid(s.replace('()', ''))

elif ('[]' in s):

return self.isValid(s.replace('[]', ''))

elif ('{}' in s):

return self.isValid(s.replace('{}', ''))

else:

return False

class Solution(object):

def isValid(self, s):

stack = []

for c in s:

if c=='(' or c=='[' or c=='{':

stack.append(c)

elif c==')':

if stack and stack[-1]=='(':

stack.pop()

else:

stack.append(c)

elif c==']':

if stack and stack[-1]=='[':

stack.pop()

else:

stack.append(c)

elif c=='}':

if stack and stack[-1]=='{':

stack.pop()

else:

stack.append(c)

return len(stack)==0