Valid Parentheses

bool isValid(string s) {

        unordered_map<char, char> brackets = {
        {'(', ')'},
        {'{', '}'},
        {'[', ']'} };

        stack<char> bracketStack;

        for (int i = 0; i < s.size(); ++i)
        {
            if (brackets.find(s[i]) != brackets.end())
            {
                bracketStack.push(s[i]);
            }
            else if (bracketStack.empty())
            {
                return false;
            }
            else
            {
                char ch = bracketStack.top();
                bracketStack.pop();
                if (brackets[ch] != s[i])
                {
                    return false;
                }
            }
        }
        return (bracketStack.empty());
    }
};