I started leetcode 3 years back. I was not that much consistent initially. My plan was to just learn some data structure and algorithms. I started with some easy problem.
After gaining some confidence I learned how to solve tree datastructure for like a month or two. Learned how to think recursively. Started visualizing the problems.
Then started solving other data structure linkedlist, binary search, Map, Set, Stack, Queue eventually. I have done this for like three month and started growing my data structure skills.
Till then I had to see most of the solutions. I wasn't able to come up with the idea. Then there was a huge break of my training session. About a year I didn't solve any problems.

round 2:
I went for interviews at amazon, google. Obviously I had no practice and I flunked. I started solving leetcode problem again. But this time I created new session at leetcode profile and started coming up the solution by myself. I solved about 150 problems and again for some reason there was huge break of my practice I didn't practice about six month.

round 3:
In the mean time I started getting email from a facebook recruiter. He kept sending email almost every month once. I had fear of interviews, that is why I was posponding. One day I thought lets just get it over with. I went for an phone interview without having much practice. This time I was able to pass that interview and went for onsite after a month. I was going there for an experience. But I figured If I had tried little bit harder I could have nailed it. That is when I started interviewing every company and every time I knew I went one step closer to the destination. I tried a year interviewing all those big companies Amazon, Google, Microsoft, Audible. But every time I was flunking out from the onsite interview. Sometimes because of system design, sometimes behavioral interview was the culprit. At last I went for facebook again after a year. After the interview I knew this time it worked for me and kept my finger crossed. Finally after a week recruiter told me I got selected.

Thanks to leetcode. I have solved over 300 problems as many ways as I can possible solve. New mock contest section is really good and also leetcodes explore section company wise problems helped me a lot. My suggestion would be don't try to memorize the problems. Try to think the problem as a new problem even if you know the problem. Cause mostly interview time it will never be common.

Phone interview:

• https://leetcode.com/problems/add-strings
• https://leetcode.com/problems/valid-palindrome-ii

Onsite Interview:

Round 1:

• https://leetcode.com/problems/best-time-to-buy-and-sell-stock
  follow up:
  • https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iii
  • https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv

Round 2:

• Design instagram client side.

Round 3:

• https://leetcode.com/problems/add-and-search-word-data-structure-design

Round 4:

• behavior
• https://leetcode.com/problems/merge-sorted-array

Round 5:

• https://leetcode.com/problems/maximum-subarray
• https://leetcode.com/problems/serialize-and-deserialize-binary-tree without using preorder, inorder, or postorder