I am a technical lead in a service based company but previously worked with product based organization. I have overall 12+ years of experience in Mobile app development and backend development. I am a full stack engineer.

I am trying hard to change my job to tier 2 companies. I have given around more than 8-10 interviews but there is no luck till now. Most of the time i got rejected either in the last round or second last round. I could not understand exaclty what wrong is going on? Can anyone please help me out how to do stream line prepration. Below are my current situtation.

1. Solved 85 leet code problems till now. I still could not solve myself most of the medium problems. some times i can solve easy problems without much hint but difficult me to solve medium problem. Impossible to solve hard as of now.
2. I could not solve with better time complexity if that particular data structure question is new for me. Is the same problem happen for other folks as well?
3. Sometimes I able to manage data structure and algo problems but then rejected in the design round. How to do prepare well in the design round? Any reference will be appreciated.

Please help me how to convert last rounds rejection to an offer?

1. RedBus: Reached till 4th round. After that got rejection mail from HR
2. BigBasket: Reached till CTO round again got rejection mail from HR
3. GoJek: Cleared couple of coding rounds, rejected in design round
4. Microsoft: Cleared one coding round but rejected in the next coding round. They asked me to print spiral matrix. I never went to this question so could not solve it at run time.
5. SmartLook: Got rejected in the 5th technical round
6. Lowes: Got rejected in the 3rd round. Here i rejected in the design round. Although i tried my level best but somehow interviewer was not convinced.
7. Ola: Got rejected in the 3rd technical round. He asked me to merge n sorted array to single array. I never solve this question before an interview so could not solve at run time as well.

I understand that for a coding round that either we will able to solve it or not able to solve it. At least we know most of the time result after coding review. I feel design interview is more tougher. We provide the answers but most of the time don't know what interviewer wants to listen. If he doesn't get agree, most of the time it goes to a negative.

Sometimes i feel demotivated and don't know how to proceed further. Now a days it's become more habitual to me reject in the last rounds :(

Any help in this will be appreciated.