Graph

Graph problems model entities and their connections, then ask about paths, reachability, components, or cycles. The first decision is the representation (adjacency list versus matrix); the second is which traversal — BFS, DFS, or a shortest-path algorithm — fits.

12 LeetCode problems solved with the Graph pattern. Practice them with spaced repetition so the pattern sticks.

• Cheapest Flights Within K StopsMEDIUM · O(k * E)
• Clone GraphMEDIUM · O(V + E)
• Course Schedule IVMEDIUM · O(n^3 + q)
• Evaluate DivisionMEDIUM · O(q * (n + e))
• Find the Town JudgeEASY · O(n + e)
• Min Cost to Connect All PointsMEDIUM · O(n^2)
• Minimum Height TreesMEDIUM · O(n)
• Network Delay TimeMEDIUM · O(E log V)
• Number of ProvincesMEDIUM · O(n^2)
• Path With Minimum EffortMEDIUM · O(R*C*log(maxH))
• Reconstruct ItineraryHARD · O(E log E)
• Swim in Rising WaterHARD · O(n^2 log n)