Poison

20. Valid Parentheses

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class Solution {
    public boolean isValid(String s) {
        if ((s.length() & 1) != 0) {
            return false;
        }

        Stack<Character> stack = new Stack<>();

        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            switch (c) {
                case '(':
                case '{':
                case '[':
                    stack.push(c);
                    break;
                case ')':
                    if (stack.isEmpty() || stack.pop() != '(') {
                        return false;
                    }
                    break;
                case '}':
                    if (stack.isEmpty() || stack.pop() != '{') {
                        return false;
                    }
                    break;
                case ']':
                    if (stack.isEmpty() || stack.pop() != '[') {
                        return false;
                    }
                    break;
                default:
                    throw new IllegalArgumentException("Unsupported char: " + c);
            }
        }

        return stack.isEmpty();
    }
}
Reference

20. Valid Parentheses