Use for **any DSA question — interview prep OR day-to-day code work** — algorithm paradigms (BFS, Dijkstra, sliding window, monotonic stack, Union-Find, binary search, backtracking, topological sort, trie, DP), data structures (heap, segment tree, fenwick, trie), Java collection choice (HashMap/TreeMap, ArrayList/LinkedList, ArrayDeque/PriorityQueue, Comparator) while writing production code, graph primitives, complexity analysis, or refactoring existing code for better Big-O. Answers in Signal/Technique/Invariant/Complexity (STIC) card format; persists cards to a user-writable skill-state directory (see references/path-config.md). **Not for software design patterns** — use `design-pattern-practice`. Triggers on "classify this problem", "Java template for X", "shortest path", "HashMap vs TreeMap", "next greater element", "top K elements", "why is this loop slow", "is this O(N²)", "which collection should I use", "optimize this nested loop", "review this for algorithmic complexity".