SRE first round interview

1. Tell me about your most recent production incident experience.
2. How did you find the root cause?
3. How would you find the root cause if your method from question 2 was not available?
4. How to troubleshoot DNS issue.

Technical

1. Valid TikTok emails are of the form user@tiktok.com, and the characteristics of user are: It starts with 1 to 6 lowercase English letters denoted by the character class [a-z]. The lowercase letter(s) are followed by an optional underscore, i.e. zero or one occurrence of the underscore '_' character. The optional underscore is followed by 0 to 4 optional digits denoted by the character class [0-9]. Domain is always tiktok.com. Complete the code in the editor below by replacing the blank (" ") with a regular expression that matches a valid email addresses according to the criteria above. Locked code in the editor prints True for each correct match and False for each incorrect match.
2. Given list of strings, concatenate those strings into the alphabetically smallest string possible. For example, 'a' < 'b', 'ab' < 'ac' and 'ab' < 'abc'