I got this interview after attending a career fair that my university hosts each semester.

During the career fair, I spoke with representatives from Facebook. Less than a week later, I received an email stating I had been selected for an interview.

The interview was scheduled for about a week after I received that email. It was an in-person, one-on-one, 50-minute interview.

The interviewer was a software engineer who worked at the Instagram branch of Facebook.

The interview went well, but it wasn't flawless. It took me longer to come up with a solution than it should have.

Thus, unfortunately, I wasn't chosen for the next phase of the hiring process.

Write a function that takes a string and determines whether the string is valid or not. The string consists only of '[', ']', '{', '}', '(', and ')'. A string is valid only if for every opening bracket or parenthesis there is a matching closing bracket or parenthesis.