Exp: 6 months Internship

Interview process:
4 rounds by { SDE2, SDE2, SDM, SDM (IDK this) }.

First 3 rounds were excellent as i had answered everything and for coding problems given approaches from brute then optimal.

Round 4:

Problem1:
It was a very basic problem even a 9th grade kid have solved it and i started to explain (like previous rounds from brute to optimal).
Optimal approach: I used a prefix sum 1D - array naming it dp[] but he used to say its not dp question then i chnged it pref[] but he said you are changing it now then i told him prefix sum is the basic dp. Then again he said its space complexity will be O(N^3). I tried to explain him its O(N) SC, but he is no mood to understand it and repeatedly replying its O(N^3). I mean how a single pref[N] can be O(N^3). At that time i understood my interview got f#d up. Then he said leave it write the code for 1st approach(brute) you came. I wrote the code and again he made a mistake in the for loop(yes in the brute force solution) and my solution is right but idk he was not accepting it.

Problem2:
This is the first problem since round1 in which I directly gave the optimal approach as time was less.
I told him I will use a while loop and go to every node of BT once and told him the approach. but here also he was like its time complexity will be O(2N) not O(N) and with a lot of confidence(why? bc solved it 1 day before Round4) told him its O(N) not O(2N) then after sometime i covinced him, he said okay what will be SC, i told him O(X + 1) he told me it will be O(X + 2) and yes atlast he was right it will be + 2 not + 1. Thats how my round 4 goes.

What shall I do in this type of interview where the interviewer is not understanding my solution in anyway. IDK how he passed leadership principle questions in his own interview.

I checked all my solutions after R#4 all were right.

Result:
Reject (7 days after interview).

PS:
Sorry for my bad English.