Given a string s 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.
Example 1:
Input: s = "()"
Output: true
Example 2:
Input: s = "()[]{}"
Output: true
Example 3:
Input: s = "(]"
Output: false
Constraints:
-
1 <= s.length <= 104 -
sconsists of parentheses only'()[]{}'.
SOLUTION:
class Solution:
def isValid(self, s: str) -> bool:
stack = []
validPairs = ['()', '[]', '{}']
valid = True
for bracket in s:
if bracket in [b[0] for b in validPairs]:
stack.append(bracket)
else:
if len(stack) > 0:
if (stack.pop() + bracket) not in validPairs:
valid = False
break
else:
valid = False
break
if len(stack) > 0:
valid = False
return valid
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