Valid Parentheses

Given a string s containing only the characters (, ), {, }, [ and ], determine if the input string is valid.

An input string is valid if:

1. Open brackets are closed by the same type of brackets.
2. Open brackets are closed in the correct order.
3. Every close bracket has a corresponding open bracket of the same type.

• Implement a function that takes a string s.
• Return true if the string is valid, false otherwise.