First Round

1. You are given a string s containing only the characters '(', ')', and '*'. Write a function to check if the string is valid.

Rules:

• Every '(' must be closed by a ')'.
• Every ')' must have a corresponding '('.
• The '*' can be treated as:
  • '('
  • ')'
  • an empty string

Your goal is to determine if the string can be valid by treating each '*' in the most beneficial way.

1. Given a string s containing only digits, return the number of ways to decode it. Each digit or pair of digits represents a letter.

Second Round

1. Explain project.
2. Design notification system (LLD).