Leetcode is the only thing that gave me the best bang for the buck. I literally tripled my salary (now $300k, USA) in 4 years because of Leetcode. I was hesitant to do Leetcode at first.
As for rejection, just keep going at it, and eventually you'll develop a thick skin.
Btw, I was rejected 9 times from programming bootcamps when I first started learning programming. I got rejected by Google 4 times, Amazon 3 times, Facebook 2 times, Uber 2 times, etc.
I don't work at any of the big tech or unicorns right now, and boy I'm glad I don't. I work at a private investment firm (still doing software). Better problems, better environment.
From not knowing that string (in JS) is immutable, to $300k/year.
Thank you Leetcode.