BFS / DFS

Breadth-first search explores level by level (shortest path in an unweighted graph); depth-first search goes deep first (reachability, connected components, backtracking). Both visit every node once — the choice is about order, not coverage.

27 LeetCode problems solved with the BFS / DFS pattern. Practice them with spaced repetition so the pattern sticks.

• 01 MatrixMEDIUM · O(m * n)
• Average of Levels in Binary TreeEASY · O(n)
• Binary Tree Level Order TraversalMEDIUM · O(n)
• Binary Tree Level Order Traversal IIMEDIUM · O(n)
• Binary Tree Right Side ViewMEDIUM · O(n)
• Binary Tree Zigzag Level Order TraversalMEDIUM · O(n)
• Find Bottom Left Tree ValueMEDIUM · O(n)
• Find Largest Value in Each Tree RowMEDIUM · O(n)
• Flood FillEASY · O(m * n)
• Keys and RoomsMEDIUM · O(n + e)
• Max Area of IslandMEDIUM · O(m*n)
• Maximum Level Sum of a Binary TreeMEDIUM · O(n)
• Minimum Depth of Binary TreeEASY · O(n)
• Minimum Genetic MutationMEDIUM · O(B * L * 4)
• N-ary Tree Level Order TraversalMEDIUM · O(n)
• Nearest Exit from Entrance in MazeMEDIUM · O(m * n)
• Number of IslandsMEDIUM · O(m*n)
• Open the LockMEDIUM · O(N^2 * A^N + D)
• Pacific Atlantic Water FlowMEDIUM · O(m*n)
• Path SumEASY · O(n)
• Populating Next Right Pointers in Each NodeMEDIUM · O(n)
• Reorder Routes to Make All Paths Lead to the City ZeroMEDIUM · O(n)
• Rotting OrangesMEDIUM · O(m*n)
• Snakes and LaddersMEDIUM · O(n^2)
• Surrounded RegionsMEDIUM · O(m * n)
• Walls and GatesMEDIUM · O(m*n)
• Word LadderHARD · O(N * L^2)