1582 articles
Find the one element that appears once while every other appears twice. The XOR bit trick delivers O(n) time and O(1) space — no extra memory, no sorting. Master the three XOR properties that make it work, then see how interviewers escalate to Single Number II and III.
Two problems, one pair of concepts: LC 349 asks for the unique intersection (HashSet), LC 350 asks for the frequency-aware intersection (HashMap). Master all three approaches for LC 349 — HashSet, sort+two pointers, binary search — then learn why the follow-up questions on LC 350 are what Google and Amazon actually care about: sorted input, skewed sizes, and data that does not fit in memory.
Master cheatsheet of all 100 Arrays & Strings problems: patterns, time/space complexity, and MAANG company tags in one place.
Master Pascal's Triangle (LeetCode 118 & 119) by understanding the binomial coefficient connection, the row-by-row DP pattern, space-optimized O(k) single-row generation, and five hidden mathematical properties that show up in Unique Paths, Coin Change, and beyond.
Master LeetCode 242 Valid Anagram with three approaches — sort O(n log n), 26-element frequency array O(n)/O(1), and HashMap O(n)/O(k). Includes a visual dry run, the critical Unicode follow-up, and the direct connection to Group Anagrams (LC 49).