dsa2 min read
Running Sum of 1D Array — Prefix Sum Foundation [Amazon Easy]
Compute running (prefix) sum in O(n) time O(1) extra space. The prefix sum pattern is foundational for range queries, subarray problems and 2D matrices.
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dsa14 min read
3Sum — The Deduplication Problem Every FAANG Interviewer Loves [LC 15]
Learn why 3Sum is a FAANG interview staple — how sorting enables two pointers, why deduplication trips up even strong candidates, a full visual dry run, and every common bug explained with Python and JavaScript solutions.
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dsa15 min read
Container With Most Water — Greedy Two-Pointer Proof [Google, Amazon, Meta]
LeetCode 11 explained from scratch: why this is a greedy problem, the formal proof that you must always move the shorter pointer, a full step-by-step dry run, common traps, and clean Python + JavaScript solutions. Master the pointer-elimination pattern that appears throughout FAANG interviews.
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dsa15 min read
Product of Array Except Self — The Prefix × Suffix Trick That Google Loves
LeetCode 238 is one of the most frequently asked medium problems at Google and Meta. Learn why the no-division constraint is intentional, how the prefix × suffix insight unlocks the O(n) solution, and how a single running variable eliminates the extra O(n) space entirely.
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dsa12 min read
Merge Intervals — The Definitive Guide (LeetCode 56) [Google, Meta, Amazon, Microsoft]
Master the classic Merge Intervals problem (LeetCode 56) asked at Google, Meta, Amazon, and Microsoft. Learn why sorting by start time is the key insight, the exact overlap condition (c ≤ b), a step-by-step visual dry run, 4 common mistakes, Python and JavaScript solutions, and follow-up problems including Insert Interval, Non-overlapping Intervals, and Meeting Rooms II.
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