15 Dec 20. Valid Parentheses
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.
- Every close bracket has a corresponding open bracket of the same type.
Example 1:
Input: s = "()" Output: true
Example 2:
Input: s = "()[]{}"
Output: true
Example 3:
Input: s = "(]" Output: false
Constraints:
1 <= s.length <= 104sconsists of parentheses only'()[]{}'.
class Solution:
def isValid(self, s: str) -> bool:
dictionary = {
“{“:”}”,
“[“:”]”,
“(“:”)”
}
stack = []
for i in s :
if i in dictionary:
stack.append(i)
elif len(stack) == 0 or dictionary[stack.pop()] != i:
return False
return len(stack) == 0
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