Problem Statement
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:
def isValid(self, s: str) -> bool:
if not s: return True
matches = {']': '[', '}': '{', ')':'('}
stack = []
for char in s:
if char in matches.values():
stack.append(char)
elif char in matches.keys():
if len(stack)==0 or stack[-1]!=matches[char]:
return False
stack.pop()
return len(stack)==0
