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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.
Two Sum (Banking)
You're auditing a set of transaction amounts and need to find two transactions that together reconcile to exactly `target`. Return the 0-based indices of the two transactions. Exactly one solution exists.
Reverse a String
Reverse a given string without using Python's built-in slice `[::-1]` — demonstrate the two-pointer technique.
Group E-Commerce Orders by Customer
You're given `n` order lines from an online store. Each line has a customer ID and an amount. Compute the total revenue per customer and print customers in ascending order of ID.
Longest Substring Without Repeating
Given a string, return the length of the longest substring with all distinct characters. Classic sliding-window problem.
Build an LRU Cache
Implement an LRU (Least Recently Used) cache with O(1) `get` and `put`. Used by every web browser, CDN, and database query planner.