20. Valid Parentheses

1 Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
2 
3 The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

给一串只包含有'(', ')', '{', '}', '[' 和']',的字符串，要求判定是否是合法的。

 1     public boolean isValid(String s) {
 2         Stack<Character> seq = new Stack<>();
 3         for (Character c:s.toCharArray())
 4         {
 5             if (c=='(') seq.push(')');
 6             else if (c=='[') seq.push(']');
 7             else if (c=='{') seq.push('}');
 8             else if (seq.isEmpty() || seq.pop()!= c) return false;
 9         }
10         return seq.isEmpty();        
11     }