unreasonably effective

class Solution:
    def isValid(self, s: str) -> bool:
        pair_of = defaultdict(str, {")": "(", "}": "{", "]": "["})
        stack = []
        for c in s:
            if stack and stack[-1] == pair_of[c]:
                stack.pop()
            else:
                stack.append(c)

        return not stack

class Solution:
    def is_matching_pair(self, i, j, s) -> bool:
        if i < 0:
            return False
        return (
               (s[i] == "(" and s[j] == ")")
            or (s[i] == "{" and s[j] == "}")
            or (s[i] == "[" and s[j] == "]")
        )

    def isValid(self, s: str) -> bool:
        s = list(s)
        i = -1
        for j in range(len(s)):
            if self.is_matching_pair(i, j, s):
                i -= 1
            else:
                i += 1
                s[i] = s[j]
                
        return i == -1