Disclaimer: This post will be long because it has my journey, interview experiences, and asks help from the community.
Also, this post is not intended to discourage anyone, this is purely what I experienced and based on my journey.

Title: Quant Engineer
Company: Reputed Bank
YOE: 2 yrs
Education: Tier 1 college
Location: India

It all started a year back on the same day. I realized that I am more interested in working as a Software Engineer and not as a Quant Engineer and wanted to shift to a Product based company ASAP.
So I started leetcoding again ( I had done inteiewbt ( Completely) + leetcode ( around 300 problems )in my college years). I started from the very basic as I was out of touch from Coding and Algorithms.
The working hours in my team are way too high and I knew it would be difficult for me to manage both. But I was extremely determined to switch to a Tech-based company and hence made a proper plan to revise and code between 11:30 pm - 1:30 am/2:30 am ( this was not a choice but the only option I had).
So started back with interviewbt and had a plan to complete it in 1 month so that I can start applying to some companies. The month went by and I missed my deadline of 1 month but completed it in 2 months.
I thought I was now a bit prepared but most of the companies had stopped hiring at that time due to COVID.
But still, I used to check Linkedin daily to know if any company is hiring. Since I had finished interviewb*t I moved on to Leetcode. Days passed by and I used to make it a target of solving at least 2-3 questions daily on weekdays and as many as possible on weekends.
Days passed by and around June Mid I did come across an opening in Microsoft and I asked one of my friends to refer me for the same. By this time I was confident in solving questions and coding but lacked speed.

So I started to compete in the contests in Leetcode, I had previously competed in a contest at leetcode and hence I started with a rating of 1640.
The first contest I gave was a disaster, was only able to solve 2 questions and ended up with a rank of nearly 5k. It did shatter my confidence a bit, but I knew if I gave the contest regularly I would improve.
Time flew by with me doing leetcode and giving every biweekly and weekly contest by this time I had reached a rating of around 1727.

On around July 20th, I received a call from the Microsoft recruiter that they want to go ahead with my candidature and scheduled around 4 interviews in the next week. I was excited as well as nervous because I had been rejected before by Microsoft during my college day.
I wanted to ace this chance anyhow. Started coding extensively on weekends and tried to give excuses to leave around 9:30 pm so that I can get a bit more time on weekdays.
On the day of the interview, I had taken leave so I woke up a bit late and did some exercise ( have heard that light exercise before the interview can be great ).

Microsoft

• 1st round: Simple question on topological sorting coded up in 10 min and walked the interviewer through it with some test cases, then the next was asked was on backtracking initially stumbled a bit but the idea clicked me and coded up quickly and walked interviewer through the tests. The interviewer was happy about it. Then he asked me a question on OS, as I knew Microsoft focuses on core CS concepts I did read up on OS but the question asked was something to which I did not know the answer. He then asked another question on OS and the same thing I replied I am not sure of this concept. The interviewer finished the interview and asked if I had any questions for him. I did ask him general questions like how is it like working in Microsoft? how is the work of the team?
• 2nd round: This question had based on insertion and deletion on a data structure -> https://leetcode.com/discuss/interview-question/363945/Google-or-Treap. I gave some ideas but it did not work out and we ran out of time.
• 3rd round: This was a system design interview. I had not prepared for system design by this time and screwed it up.
• 4th round: Hiring manager round. He asked a simple question on String to which I coded up quickly. He then asked about concepts of OS, OOPS, Pointers, References, I did not know much about these. As I don't use all this in my current job and also in my college days even though I read about them but I don't remember them and I did not revise them.
• Result: As expected I was rejected.
  I felt a bit sad but I at least I knew what had gone wrong and what to focus on.
  So I tweaked my plan a bit and added 2 days to study core CS concepts like OS, DB, CN, OOPS, Design Patterns.

Days passed by with my coding and learning this stuff. I could see my efforts giving fruits at least that's what I thought as my rating was increasing and I was able to a solve 3 question in every contest.
On the last week of August, I came across that Flipkart was hiring for SDE 1 roles. I asked one of my friend for a referral.
Got a call in a week that they want to go ahead with rounds. This time I saw the format and previous question asked in Flipkart from GFG. Did some practice of the machine coding round as it was my first round.
By this time I was rated around 1850in leetcode

Flipkart:

• 1st round ( Machine Coding ): Question on designing and implementing an uber like cab service was asked. I clarified the expectations of the service and gave my approaches. The interviewer was happy with the approach and he asked me to code it up.I quickly coded up the solution and dry ran it through various cases. He then asked few cases from his side all of them passed except one, which was like a weird edge case that I did not handle. I quickly fixed that. We were right before time so we discussed on his work at Flipkart and his experience.
• Result: Qualified this round and they proceeded me for the next round which was based on DSA.
• 2nd round ( DSA ): Interviewer started with a question https://leetcode.com/problems/largest-rectangle-in-histogram/, I came up with the most optimal solution and code up quickly. He then asked a question that could be solved using Binary search( Not on leetcode ), I also gave the most optimal solution for this and coded it up. Then he asked a question that could be solved by DP (Not on leetcode) same as before I coded it up optimally.The interviewer was quite impressed and since time was left we discussed again his work at Flipkart and his team
• Result: Ghosted, I tried reaching every week for 3 weeks but no response. I thought I have been rejected and stopped mailing the recruiter for updates. Reason: unknown.

At this time I was a bit broken as I did not know what was my fault and what I could have done better.
But I picked up myself and started coding as I had Amazon coding round ( asked for Referral through my friend during these 3 weeks).

Amazon:

• Online coding: Two questions were asked, was able to code it up quickly and most optimally.
• Result: Selected for Onsite.
• Onsite:
• 1st: round: https://leetcode.com/problems/max-area-of-island/ && https://leetcode.com/problems/maximum-product-of-splitted-binary-tree/ and leadership question on the current project. Coded upmost optimally both the solutions
• 2nd round: Implement stack using queue and 2 leadership question on current works
• 3rd round: Binary search tree insertion, search and deletion ( Not balanced BST ), and leadership questions.
• 4th round: Purely Leadership round as far as I remember.
• 5th round: One question that could be solved by Trie and another question on DP.
• Result: Selected but I had to reject the offer since they were paying me nearly 8 lakh rupees less than what I earn now. Tried to negotiate but they did not accept and hence had to drop this offer.

At this time I was broken and a bit happy. Happy that I was able to crack Amazon which I could not during my college time and broken because I couldn't join it, also Amazon recruiter said me that no Tech company including Google will pay me what I expect so was a bit worried. But I had seen my teammates leaving to google for a higher salary.
So I decided to target Google. I knew Google was not easy at all, I had previously applied to google 5 times but never got a call for an interview. I did not know how I could end up with an interview at Google.
With all this going on I parallelly used to give Google kickstart could secure a rank of nearly 1k but I knew this would not get me a call. So I decided to level up my coding skills, I focused on hard questions from Leetcode and previous year's questions from Codejam and Kickstart now.
Initially, they were quite tough ( In fact they are tough now also ) could take me a day or two and I could not come up with the solution, and some involved concepts like Bipartite matching which I never focused on as I knew Companies usually don't ask advance topics like this, I think Google also never asks the question on this topic at least in the interview, correct me if am wrong.
But I did not want to take a chance so I started learning these concepts like Bipartite matching, Flows, Suffix array, and so on. By this time I was well prepared with concepts like OS, DB, CN, OOPs so I decide to learn these concepts on the days I kept for studying Core concepts.
I start practicing questions from Lightj and Codeforcs, also continually gave contest on Leetcode.
Days passed by and my rating in Leetcode was now 2041. I could nearly solve 4 questions and ranked nearly among the top 300-400 always. My kickstart for the last round was nearly 600 ( the best). I knew it would still be difficult to get a call from Google but I thought to try for the next Kickstart and Codejam starting March this year.
All this while I applied to Google around 2 times ( 6 positions, as one referral, allows you to apply for 3 positions). And as always got rejected. I always doubted myself and kept going hoping one day I will reach where i want to be.

Sometime in the first week of February i got calls from Cohesity ( asked for Referral from one of my friends around September 2020), Microsoft ( again asked for a referral around January mid as I was done through their freezing period of 6 months),
Bloomberg ( Frankfurt office ( again took a referral from a Friend)) and surprisingly Google( just tried my luck with one more referral with no hopes ).
I was super excited and somewhere in my mind, I was confident that this time I will be able to it.

Cohesity:

• 1st round: https://leetcode.com/problems/two-sum-iv-input-is-a-bst/ & https://leetcode.com/problems/check-completeness-of-a-binary-tree/ Coded up optimally both the questions.
• 2nd round: Desing a Garbage collector. Had a discussion with the interviewer on multiple approaches.
• Result: Ghosted, again tried reaching recruiter every week for 3 weeks but no luck. Assumed I have been rejected and moved on.

Bloomberg:
Was scheduled for 1st round in 2 weeks. 2 weeks later I got a call from the recruiter that they have filled in the position and will not be able to move ahead.
Extremely disappointed and sad but had to move on hoping that I get selected in Microsoft or Google.

My next interview was again with Microsoft and this time I had prepared for OS, DB, CN, OOPs, and a bit on System design so was a bit confident.

This time my interview was 2 rounds on one day and if these goes well then the recruiter said she would schedule the other 2 rounds.
Microsoft:

• 1st round: https://leetcode.com/problems/sudoku-solver/. Coded up quickly and completely then the interviewer asked questions on Security which I did not prepare upon. I was broke in the interview itself as and when he asked this question, had my self up and told him some approaches but he was not satisfied and asked another question related to security to which again I gave some answer which he was not satisfied.
• 2nd round: 3 questions,
• 1. Given an array find the peak element ( peak element is defined as an element that is greater than both elements on either side if they exist). I quickly gave a trivial O(N) solution but he wanted a better solution. I asked if the array was sorted and reverted or some kind of info he said no just given a random array. I thought about it for a time but could not come up with it, he said its ok move on.
• 2. https://leetcode.com/problems/minimum-cost-to-cut-a-stick/ Coded optimally
• 3. One question on the Sliding window, ( not on leetcode) Coded optimally
• All the questions should be coded from scratch including things like taking input and printing output in own IDE and should compile properly the interviewer gave test cases to check the correctness of the program.
• Result: Ghosted, again tried to follow up with recruiter for 3 weeks and assumed that I have been rejected.

By this time I have lost all my confidence as apart from the above companies that I interviewed for I applied to a lot of companies like Adobe, Intuit, Indeed, Salesforce to just name a few, and got rejected in the resume screening.
I just had one last chance and hope and that Google. I had lost all my confidence but I did not want to lose this chance so I picked up myself and gave one last shot.

By this time I was rated 2109 on leetcode

Google:

• Telephonic: One question on Sliding Window ( Not on leetcode) I took some time to discuss the algorithm and coded it and dry ran the code. The interviewer was satisfied but I was 5 min late. The interview was for 45 min but I completed it in 50 min.
• Result: Moving to Onsite, Recruiter mentioned that I need to speed up a bit.
• Onsite:

•   1st round: One question on math, I was able to come up with the most optimal solution and coded it up and dry ran for various test cases. The interviewer seemed satisfied. I was worried because I was able to do only 1 question and I thought Google expects no less than 2 questions.

•   2nd round: This was my best round had solved 3 questions optimally, based on DFS, Graph, and Trees

•   Result: Recruiter told that both the interviews were positive and they wanted to take 2 more interviews

•   3rd round: Googlyness, questions on my past project, and background.

•   4th round: This was the worst round for me one question based on Greedy was asked, I was able to come with the most optimal solution but required help from the Interviewer. 

•   Result: Just got to know today I was rejected and need to focus on DSA.

If you have come this far. Thanks a lot for reading this.

I am completely broken now. I had tried my best and I am completely not sure what I have to do next.
Doing DSA for another year would be difficult as my job demands high working hours and this one year I have given up on multiple things to achieve this goal.
Have given up on my health and sleep just to achieve this.

I am grateful to this community, especially the disscuss section.
I would ask the Leetcode community to help me and suggest what I can do next? I am totally confused and broken as this has happened to me before during my college days and I somehow just managed to get into my current Quant Role. I am worried that even if I somehow manage to code for an extra year would that be beneficial ?, I was able to come up with the most optimal solution in most cases but for reasons unknown, I was rejected. I am not sure what I can do to just get that one good offer.