Explore

Graphs

✅ Step 1: Graph Basics + BFS/DFS Foundations

Build intuition around graph traversal and adjacency list representation.

Number of Provinces —

https://leetcode.com/problems/number-of-provinces/⁠

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Flood Fill —

https://leetcode.com/problems/flood-fill/⁠

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Max Area of Island —

https://leetcode.com/problems/max-area-of-island/⁠

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Number of Islands —

https://leetcode.com/problems/number-of-islands/⁠

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Rotten Oranges —

https://leetcode.com/problems/rotting-oranges/⁠

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Is Graph Bipartite? —

https://leetcode.com/problems/is-graph-bipartite/⁠

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Surrounded Regions —

https://leetcode.com/problems/surrounded-regions/⁠

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Walls and Gates —

https://leetcode.com/problems/walls-and-gates/⁠

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Pacific Atlantic Water Flow —

https://leetcode.com/problems/pacific-atlantic-water-flow/⁠

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✅ Step 2: Topological Sorting (Kahn’s Algo + DFS)

Used in DAGs (Directed Acyclic Graphs) — key for scheduling and ordering problems.

Course Schedule —

https://leetcode.com/problems/course-schedule/⁠

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Course Schedule II —

https://leetcode.com/problems/course-schedule-ii/⁠

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Minimum Height Trees —

https://leetcode.com/problems/minimum-height-trees/⁠

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Find Eventual Safe States —

https://leetcode.com/problems/find-eventual-safe-states/⁠

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Minimum Number of Vertices to Reach All Nodes —

https://leetcode.com/problems/minimum-number-of-vertices-to-reach-all-nodes/⁠

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Sort Items by Groups Respecting Dependencies —

https://leetcode.com/problems/sort-items-by-groups-respecting-dependencies/⁠

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✅ Step 3: Detecting Cycles (Directed + Undirected)

Essential for checking validity in graphs (safe states, deadlocks, etc.)

Detect Cycle in a Directed Graph (Course Schedule II) —

https://leetcode.com/problems/course-schedule-ii/⁠

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Find Eventual Safe States —

https://leetcode.com/problems/find-eventual-safe-states/⁠

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Reconstruct Itinerary —

https://leetcode.com/problems/reconstruct-itinerary/⁠

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Find the Town Judge —

https://leetcode.com/problems/find-the-town-judge/⁠

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Find Center of Star Graph —

https://leetcode.com/problems/find-center-of-star-graph/⁠

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✅ Step 4: Shortest Path Algorithms (BFS, Dijkstra, Bellman-Ford, 0-1 BFS)

Critical for routing, cost-based traversal.

Shortest Path in Binary Matrix —

https://leetcode.com/problems/shortest-path-in-binary-matrix/⁠

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Path With Minimum Effort —

https://leetcode.com/problems/path-with-minimum-effort/⁠

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Dijkstra: Network Delay Time —

https://leetcode.com/problems/network-delay-time/⁠

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Dijkstra: Cheapest Flights Within K Stops —

https://leetcode.com/problems/cheapest-flights-within-k-stops/⁠

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Bellman Ford: Cheapest Flights Within K Stops —

https://leetcode.com/problems/cheapest-flights-within-k-stops/⁠

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0-1 BFS: Shortest Path with Alternating Colors —

https://leetcode.com/problems/shortest-path-with-alternating-colors/⁠

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Minimum Cost to Make at Least One Valid Path —

https://leetcode.com/problems/minimum-cost-to-make-at-least-one-valid-path-in-a-grid/⁠

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✅ Step 5: Union Find (Disjoint Set Union - DSU)

Powerful for connectivity queries, cycle detection, Kruskal’s MST.

Redundant Connection —

https://leetcode.com/problems/redundant-connection/⁠

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Redundant Connection II —

https://leetcode.com/problems/redundant-connection-ii/⁠

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Graph Valid Tree —

https://leetcode.com/problems/graph-valid-tree/⁠

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Number of Connected Components in Undirected Graph —

https://leetcode.com/problems/number-of-connected-components-in-an-undirected-graph/⁠

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Satisfiability of Equality Equations —

https://leetcode.com/problems/satisfiability-of-equality-equations/⁠

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Accounts Merge —

https://leetcode.com/problems/accounts-merge/⁠

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Evaluate Division —

https://leetcode.com/problems/evaluate-division/⁠

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✅ Step 6: Minimum Spanning Tree (Prim’s & Kruskal’s)

Find lowest cost to connect all nodes — vital for networking problems.

Minimum Cost to Connect All Points —

https://leetcode.com/problems/min-cost-to-connect-all-points/⁠

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Connecting Cities With Minimum Cost —

https://leetcode.com/problems/connecting-cities-with-minimum-cost/⁠

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Optimize Water Distribution in a Village —

https://leetcode.com/problems/optimize-water-distribution-in-a-village/⁠

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Critical Connections in a Network —

https://leetcode.com/problems/critical-connections-in-a-network/⁠

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✅ Step 7: Backtracking + Graphs Hybrid

Graph traversal + permutations, cycles, etc.

Word Ladder —

https://leetcode.com/problems/word-ladder/⁠

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Word Ladder II —

https://leetcode.com/problems/word-ladder-ii/⁠

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Reconstruct Itinerary —

https://leetcode.com/problems/reconstruct-itinerary/⁠

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Word Search —

https://leetcode.com/problems/word-search/⁠

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Word Search II —

https://leetcode.com/problems/word-search-ii/⁠

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✅ Step 8: DP on Graphs (Memoized DFS)

Some problems are best solved via topological + memoization (DAGs mostly).

Longest Path in a Directed Acyclic Graph —

https://leetcode.com/problems/longest-path-with-different-adjacent-characters/⁠

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Longest Increasing Path in a Matrix —

https://leetcode.com/problems/longest-increasing-path-in-a-matrix/⁠

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All Paths From Source to Target —

https://leetcode.com/problems/all-paths-from-source-to-target/⁠

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Minimum Height Trees —

https://leetcode.com/problems/minimum-height-trees/⁠

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✅ Step 9: Advanced Graph Problems (Hard-Level)

Prepare for FAANG and top-tier interviews with these.

The Maze —

https://leetcode.com/problems/the-maze/⁠

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The Maze II —

https://leetcode.com/problems/the-maze-ii/⁠

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The Maze III —

https://leetcode.com/problems/the-maze-iii/⁠

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Word Search II —

https://leetcode.com/problems/word-search-ii/⁠

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Crack the Safe —

https://leetcode.com/problems/cracking-the-safe/⁠

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Remove Invalid Parentheses —

https://leetcode.com/problems/remove-invalid-parentheses/⁠

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Find the Celebrity —

https://leetcode.com/problems/find-the-celebrity/⁠

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Alien Dictionary —

https://leetcode.com/problems/alien-dictionary/⁠

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