Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.
Input
()
Output
True
Input
([)
False
False
需要靠虑算法的复杂度不能够太大