Valid Parentheses

	/**
	 * 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.
	 * 
	 * */