Valid Parentheses

You are given a string s.

Your task is to determine if the input string s is valid.

Note that:

• The string s contains only the characters: '(', ')', '{', '}', '[' and ']'.
• An opening bracket ('(', '{', or '[') must be closed by the same type of closing bracket.
• Opening brackets must be closed in the correct order. For example, ([)] is not valid because the [ is closed before the (.
• Every closing bracket must have a corresponding opening bracket of the same type.

Return true if s is valid, otherwise return false.