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Dijkstra's algorithm is four lines of greedy logic wrapped in machinery that fails quietly, so this post builds a binary-heap implementation in TypeScript, differential-tests it against Floyd-Warshall on 4,000 random graphs, and measures what the heap, the Array.shift() queue and the stale-entry check actually cost.

Union Find trades every graph question except one for speed, and measured tree heights show exactly what path compression and union by rank each buy you — with tested solutions to Redundant Connection, Number of Connected Components, and Accounts Merge.

A monotonic stack maintains elements in order and pops when that order breaks — finding the next greater element for every popped value in O(n) total.

The Two Sum problem is the "Hello World" of hash map problems. Most people solve it, move on, and treat it as a warmup. That's a mistake. The pattern behind Two Sum — trading space for lookup speed — shows up in dozens of harder problems.

Two mid-to-senior linked list problems that test data structure design: deep-copying a list with random pointers (O(1) space trick), and implementing LRU Cache in O(1).

Sliding window maximum is the classic follow-up to every sliding window problem. Learn the monotone deque pattern in JavaScript with LeetCode 239, 1438, and 1696.

LC 297 is a Hard but the insight is simple: null markers make any traversal unambiguous. Learn preorder DFS and BFS serialization, plus the BST shortcut for LC 449.

Jump Game, Gas Station, and Partition Labels — three greedy DSA patterns that feel like guesswork until you see the invariant that makes each one provably correct.

Three 1D DP patterns that show up in every senior interview: LIS, Max Product Subarray, and Word Break — with brute force, optimized, and Trie-based solutions in JavaScript.