Hi, wanted to give back to the community

I had my phone screen this past week and was asked:

680. Valid Palindrome 2.
     Follow up question: Instead of 1 character remove how would I deal with k character removal

681. Diameter of Binary Tree

Additional question:
1249. Minimum Remove to Make Valid Parentheses
Only thought process. No code

Answered the first one but fumbled with the follow up.

Second one answered with dfs. No follow ups.

Since above were easy lc questions, I finished in 20 ish mins. So was asked the third question. Only thought process.

Heard back 2 days later that I will be moving on to onsite.

If anyone has resources to prepare for onsite please let me know. My system design is not so great.

Hope this helps in any way - best of luck!