20. Valid Parentheses
https://leetcode.com/problems/valid-parentheses/description/
Given a string containing just the characters '('
, ')'
, '{'
, '}'
, '['
and ']'
, determine if the input string is valid.
An input string is valid if:
Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.
Note that an empty string is also considered valid.
Example 1:
Input: "()"
Output: true
Example 2:
Input: "()[]{}"
Output: true
Example 3:
Input: "(]"
Output: false
Example 4:
Input: "([)]"
Output: false
Example 5:
Input: "{[]}"
Output: true
Solution:
class Solution(object):
def isValid(self, s):
"""
:type s: str
:rtype: bool
"""
stack = [None]
pars = {')': '(', '}': '{', ']': '['}
for ss in s:
if ss in pars and pars[ss] == stack[len(stack)-1]:
stack.pop()
else:
stack.append(ss)
return len(stack) == 1
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