Leetcode_#20_有效的括號

原題：#20_有效的括號

public boolean isValid (String s) {
    Stack<Character> stack = new Stack<>();
    for (String c : s.toCharArray()) {
        if (c == '(' || c == '{' || c == '[') {
            stack.push(c);
        } else {
            char cStack = stack.pop();
            boolean b1 = c == ')' && cStack != '(';
            boolean b2 = c == '}' && cStack != '{';
            boolean b3 = c == ']' && cStack != '[';
            if (b1 || b2 || b3) {
                return false;
            }
        }
    }
    return stack.isEmpty();
}