Meta Onsite 3-5 YOE role

YOE: 4.5
SWE Role 3-5 YOE
Had Onsite scheduled with meta today I am not expecting offer but contributing to the community.

Phone Screen:

1. Valid Parenthesis by removing 1 element
2. Binary Tree Vertical ordering
   Cleared and got Onsite

Onsite
Round 1: Produc Design
Design a File/Folder Sync app (like Drive and dropbox)
Focused more on the API design and the schema table design went Alright

Round 2: Behavioral
Top behavioral question went Alright

Round 3: Coding

1. given m x n array print all the values or return it in a list diagonal like / / /
   ex: 1 2
   3 4
   return 1
   2 3
   4
2. Graph question given C1 -> email1, email2 ; C2 -> email3, email4; C3 -> email5, email6; C4->email1,email4
   Need to merge same contatcs and return the list of list like [[C1,C2,C4] , [C3]]
   Wasn't able to finish it but she understood what I was trying to do.

Round 4: Coding [Worst Round]

1. Given x coordinates sorted need to plant seeds with given constraints distance d.
   so to plant at a & b we need b-a >= d. (Couldn't solve but got the idea of looking back to last coord less than or equal to coord[i]-b and add the seeds at that location. Still not sure if this answer would have worked? The interviewer was there to make me self doubt any solution I suggest.)

2. Served a char character stream we need to return the first unique character we see in that order
   ex: Served on next(char c) -> a b b c a res: a a a a c.
   Solved the second question but the interviewer asked if the next(char c) method can operate in O(1) time which I had was amortized & I said No(Comment the correct answer).

I am not hoping they will extend any offer but lets see what happens. Also, please link any questions on leetcode that are related to above ones or same.