1575 articles
Master LeetCode 125 — Valid Palindrome with the O(1)-space two-pointer technique. Learn why every FAANG loop starts here, visualize the pointer walk on a classic example, avoid the four most common pitfalls, and unlock the palindrome follow-up chain: LC 680, LC 5, and LC 647.
Find the longest common prefix string among an array of strings. Covers vertical scan O(n*m), horizontal scan, binary search, and Trie approaches with all 5 language solutions.
Count the number of prime numbers strictly less than n. Master the Sieve of Eratosthenes — one of the most elegant algorithms in CS — with full code in C, C++, Java, JavaScript and Python.
LeetCode 268 hides four distinct valid solutions behind a deceptively simple problem. Learn Sort, HashSet, Gauss Formula, and XOR — understand exactly why each exists, when interviewers ask for each one, and why XOR is the most elegant answer in the room.
The Boyer-Moore Voting Algorithm solves LeetCode 169 in O(n) time and O(1) space using a brilliantly counterintuitive cancellation trick. Learn the proof, the dry run, all four approaches, and why interviewers love this problem — plus the Majority Element II follow-up that extends the same idea to two candidates.