20. Valid Parentheses

class Solution {
    public boolean isValid(String s) {
        Deque<Character> stack = new ArrayDeque<>();
        for (char c : s.toCharArray()) {
            if (c == '(' || c == '[' || c == '{') {
                stack.push(c);
            } else if (c == ')') {
                if (stack.isEmpty() || stack.peek() != '(') {
                    return false;
                }
                stack.pop();
            } else if (c == ']') {
                if (stack.isEmpty() || stack.peek() != '[') {
                    return false;
                }
                stack.pop();
            } else if (c == '}') {
                if (stack.isEmpty() || stack.peek() != '{') {
                    return false;
                }
                stack.pop();
            }
        }
        return stack.isEmpty();
    }
}