[Request] Leetcode Resources & Prep Advice for Quant Trading

Quant trading is broad. For most firms, the trading interview process doesn't include much computer science (Optiver, Jane Street, SIG, Akuna, etc.). For some firms, it is tailored to your background; you shouldn't expect much CS unless you study CS or say you know CS (example Citadel/Securities) and even then its usually pretty light that most CS majors can handle. The firms that really care about CS for their equivalent quant trader (they are really quant research) roles do care that you can code, and this is where leetcode would become relevant (example HRT, Two Sigma, D.E. Shaw). 

For some firms the quant (research) interview process usually includes CS. Leetcode can help here. I would first figure out whether you're interested in quant research or quant trading (or software, which clearly is dependent on leetcode). If you order the roles as trading - research - software, the amount of CS necessary in interviews generally increases from left to right. That isn't to say it's not helpful, but in my experience not a requirement. You should also figure out what these roles actually do.

for your questions:
1. Whatever works; presumably both end up in the same place. my intuition is that its better to have a concrete DS&A understanding then build on top with leetcode. learn how to apply. 
2. google
3. prob,stat, brainteasers, mental math (sometimes) 100% more important in most trading interviews than computer science (excluding coder-centric firms like hrt, two sig). Most major firms off the top of my head will not ask you shit about CS unless you actually study CS, and even then not much (e.g. JS, SIG, Five Rings, etc.). i'll let you figure out where you want to spend your time. If you had X amount of time to prepare and you knew little CS, i'd do 0.70X on prob,stat,brainteasers,mental math and the rest maybe on CS. not sure since i already had CS background when interviewing. In my experience most cs majors who interview for these roles (trading) have the cs background to pass the cs questions given, and prepare / had prepared using math competitions or studying probability, statistics etc.  there are a couple quant interview books that should come up, but more important to learn how to solve than to learn the solution
4. a. learn what you role(s) want to do b. learn what companies do what you want to do well c. learn what you actually need to know to get the job d. prepare 

note that the competition is pretty hard, and a sizeable portion of the time the relevant prep was done basically in HS (math, coding competitions) towards learning how to solve (or sufficiently apply knowledge to new situations). lots of other misc things to consider (how to get interviews (answer: go to hypsm, talk to hr well, get referrals, have strong resume)), some luck (anyone who says otherwise is wrong), id say have a good backup plan (try to get a return offer, which is helpful towards forcing interviews). also don't discount behavioral; sometimes its judged as part of the technical questions (how you say your answers matters). think these are the main things. easier if you have an internship in quant trading imo, but not impossible to get in otherwise. theres a lot of value in flexibility, i think (ability to solve different types of problems/ things you havent seen before). good luck. 

source: senior with some offers + friends interviewed or will/ work in the industry