The Urgent Shipment Waited Behind Ordinary Orders.
order-8841 had to leave today. The line shipped two ordinary orders first because they had been waiting longer.
One Cycle, and the Same Order Never Finished.
Packing’s next step pointed back at the order it was already in. The walk never reached a last step.
DFS Found a Path. It Was the Long One.
Inventory’s route to shipping is three hops. Notify’s is two. The search that dives deep still says it found shipping — and hands you the slow path.
Binary Trees & BSTs — Complete Guide with Interactive Walkthroughs
Binary trees, BST search and insert, DFS vs BFS, inorder, validate, and LCA — with step-through animations and a practice ladder.
Stacks & Queues — Complete Guide with Interactive Walkthroughs
Master LIFO stacks, FIFO queues, and monotonic deques — parentheses matching, adjacent duplicates, recent calls, daily temperatures, and sliding window maximum. Animations included.
Linked Lists — Complete Guide with Interactive Walkthroughs
Master linked list mechanics, fast and slow pointers, and in-place reversal — insert/delete, cycle detection, k-th from end, and swap pairs without cheating into an array. Animations included.
Binary Search — Complete Guide with Interactive Walkthroughs
Master binary search on sorted arrays and answer spaces — classic templates, lower/upper bounds, 2D matrix tricks, and O(n log k) feasibility checks. Animations included.
Hashing — Complete Guide with Interactive Walkthroughs
Master hash maps and sets for O(1) lookups — existence checks, frequency counting, prefix + frequency patterns, and grouping. The most important data structure in interview prep. Animations included.
Prefix Sum — Complete Guide with Interactive Walkthroughs
Master prefix sums for O(1) subarray range queries — build the array, answer queries in constant time, split arrays in one pass, and optimize to O(1) space. Step-through animations included.
Two Pointers — Complete Guide with Interactive Walkthroughs
Master the two pointers technique for arrays and strings — opposite ends, merge walk, palindrome checks, two sum on sorted input, and subsequence matching. Step-through animations included.
Sliding Window Technique — Complete Reference with Animations
A friendly, step-by-step guide to sliding windows — from your first two-pointer problem to monotonic deques, production rate limiters, and the at-most-K trick. Interactive animations included.