u/RaunchyPillow

Hello people, I'm writing because no matter how hard I try, I just keep failing on codeforces, I'm facing this very weird sort of thing that I'm able to solve random problem from problemset of around 1400 comfortably now most of the time, but when I give contest it does not translate at all. In yesterday's contest, I just could not get myself thinking in the right way, it felt as if I just cannot think. Mainly the issue is with greedy and constructive ad-hoc problems mostly that I've noticed. Yesterday, I prepared whole day for the evening contest, did almost 6-7 good problems on leetcode, gave atcoder contest and was able to do 4 questions there, which surely felt really good to me, then I had codeforces contest, I went in full confident, then 1st question, 3 WAs (2 of them were due to typos in my solution (yeah I'm dumb)), then I got AC, then problem B, I just couldn't do it at all. Problem C1, I had an idea, but could not implement for some reasn that I don't know. I don't know how to deal with this situation, where at times when I prepare a lot, give a ton of effort, I keep losing rating and when I just do not care, suddenly rating goes higher and higher,
I also want to know how to prove your solution before submitting, because on div2A's and B's almost everytime the intuition is correct, so I rely onto it, but this time I paid hefty for that.

I do not know whether even to continue codeforces or just shift completely to atcoder, since mostly these days codeforces contests are just greedy or ad-hoc rather than data structures or algorithms. I have around 350 problems on codeforces which is not much but I have around 250 something on leetcode, so I almost everytiem stick to codeforces so that atleast on one platform I have a good question count. With college internships coming up, I have ZERO confidence in myself that I'll be able to crack that.

Recently, I was fortunate enough to give Salesforce interview and the lady asked me a greedy problem maybe CP styled, I just could not solve that. The question was: You're give an string, and you have to reverse the string, usng the operation: "You can delete a character and append it at the end of string.", Determine the minumum operations required to reverse the string. I read the problem and was completely blank for a moment, I tried to think the minumum moves to swap two mismatched characters which was the wrong idea, and since this was the first problem she asked, I basically f'ed up my whole interview.
Please guide me some tips on what to practice, and where to practice, I'm just so confused/frustrated about all this.

EDIT: I've added the correct solution in the comments, let me know what do you think of the solution. The odea is we can always find a correct seq of the pos. that must be changed.