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Two Sum is the #1 most-asked interview problem at Google, Amazon, and Meta — confirmed in over 170 interviews at 70 companies. But it is not about the solution. It is about showing you can trade space for time, recognize the hashmap complement pattern, and handle every follow-up a senior engineer can throw at you.
Learn why LeetCode 121 is a FAANG staple — not because it is hard, but because of what it reveals about your thinking. Master the running-minimum insight, avoid the global min/max trap, and understand all five stock variants from 121 to 309.
LC 217 looks trivially easy — but FAANG interviewers use it to probe your hashset vs sorting instincts, your ability to articulate space-time trade-offs, and whether you can spot the follow-up traps in LC 219 and LC 220. Full solutions in Python and JavaScript with deep explanation.
Most explanations of Kadane's Algorithm get it subtly wrong. Learn the correct mental model, the critical reset-to-0 bug that trips everyone up, a full visual dry run, divide-and-conquer alternative, and every FAANG follow-up question with approach hints.
LeetCode 283 is the gateway to the two-pointer partition pattern used across dozens of harder problems. Learn why it appears in almost every Microsoft and Amazon phone screen, master the write-pointer mental model with a step-by-step dry run, and understand when to swap vs. overwrite — with Python and JavaScript solutions fully annotated.