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Hand-picked problems across 6 languages — banking, e-commerce, analytics, system design. Run them right in your browser; ask AI when stuck.
Serialize a Binary Tree
Serialize a binary tree to a string and deserialize it back. A classic system-design interview question — how would you transmit a tree over a network? Use level-order with `null` sentinels.
Max Subarray Sum (Stock Analytics)
Given daily profit/loss numbers for a stock, find the maximum total profit over any contiguous window of days (Kadane's algorithm — a trading interview classic).
Group Anagrams
Given a list of words, group them into anagram families. Any ordering is acceptable.
Valid Parentheses
Given a string of brackets `()[]{}`, return `true` if every opener has a matching closer in the correct order.
Coin Change (Minimum Coins)
Given coin denominations and an amount, return the fewest coins needed, or -1 if impossible.