Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
An input string is valid if:
Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order.
Example 1:
Input: s = "()" Output: true Example 2:
Input: s = "()[]{}" Output: true Example 3:
Input: s = "(]" Output: false