LeetCode/20_Valid_Parentheses.py at main · AnmolPatel20/LeetCode · GitHub

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"""
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

Example 4:

Input: s = "([])"

Output: true

Example 5:

Input: s = "([)]"

Output: false


Constraints:

1 <= s.length <= 104
s consists of parentheses only '()[]{}'.

"""
class Solution:
    def isValid(self, s: str) -> bool:

        stack = []
        for c in s:
            if c == '(' :
                stack.append(')')
            elif c == '{' :
                stack.append('}')
            elif c == '[' :
                stack.append(']')

            else :
                if not stack or stack.pop() != c:
                    return False

        return not stack