18 questions
Seed every 0 into one BFS — cell values are hops; a nearest-zero walk from each 1 is honest and quadratic, and a 0 is already distance 0.
Read MoreUnion-Find on account ids merges rows that share an email after a HashMap maps each address onto an index; an email graph plus DFS is honest extra adjacency.
Read MoreAt most k stops is k+1 edges: snapshot-relax that many rounds from src. Dijkstra that ignores the hop budget settles a cheap path that used too many flights.
Read MoreHash original node to clone, then wire neighbors through the map. A nested copy with no map duplicates nodes on cycles; a linear scan per neighbor is the honest quadratic.
Read MoreSame Kahn as Course Schedule, but append every drained course; leftovers mean return empty — permuting the catalog is honest and still factorial.
Read MoreDrain indegree-zero courses with Kahn; leftover vertices are a cycle, and permuting the catalog is honest and factorial — this prompt wants a boolean, not a sequence.
Read MoreEach unseen land cell starts one flood that returns how many cells it sank — walking neighbors with no mark never returns, and restarting a full flood from every land cell is the honest quadratic.
Read MoreManhattan MST is Kruskal on all pairs — sort, Union-Find skip same component; enumerating spanning trees is honest and combinatorial, and a shortest-path tree from one point is not that MST.
Read MoreSettle every node from k with a min-heap of distances; the signal arrives when the farthest node does, and unweighted BFS is the trap when latencies vary.
Read MoreEach unseen land cell starts one flood that sinks the component — walking neighbors with no mark never returns, and restarting a full flood from every land cell is the honest quadratic.
Read MoreUnion-Find counts leftover roots on an n×n city matrix — restarting a DFS from every city is the honest cubic, and an adjacency list stores a graph the matrix already is.
Read MoreSeed every Pacific and Atlantic border cell and walk inland to equal-or-higher heights; nested downhill search from every cell is honest and too slow.
Read MoreUnion-Find returns the first edge whose ends already share a root — adding each cable and DFS-hunting a cycle is honest and too slow.
Read MoreSeed every rotten orange into one BFS — minutes are hops; a nearest-rotten walk from each fresh cell is honest and quadratic, leftover fresh is -1, and no fresh oranges is 0.
Read MoreO's that touch the border stay; flood those first with a temporary mark, then flip leftover O to X — searching from every O whether it can reach a border is the honest quadratic.
Read MoreStart on cells that match word[0] and walk four neighbors with mark-and-undo; generating every path of length L and comparing at the leaf is honest and exponential for the wrong reason.
Read MoreRepresentation and operations — not the problem set.