1.     public boolean isValid(String s) {
    2.         final int length = s.length();
    3.         if (length % 2 == 1) {
    4.             return false;
    5.         }
    6.         Deque<Character> deque = new LinkedList();
    7.         for (int i = 0; i < length; i++) {
    8.             char at = s.charAt(i);
    9.             if ('(' == at) {
    10.                 deque.push(')');
    11.             } else if ('[' == at) {
    12.                 deque.push(']');
    13.             } else if ('{' == at) {
    14.                 deque.push('}');
    15.             } else if (deque.isEmpty() || at != deque.pop()) {
    16.                 return false;
    17.             }
    18.         }
    19.         return deque.isEmpty();
    20.     }