What is LeetCode 286 Walls and Gates about?

Fill empty rooms (INF) in a 2D grid with distance to nearest gate (0), ignoring walls (-1). Classic multi-source BFS.

How does multi-source BFS work in Walls and Gates?

Enqueue all gates at dist 0 with shared visited. BFS expands, updating mins only if closer path found.

Is LeetCode 286 hard for interviews?

Medium. Nails BFS/graph basics—expect at Google, Meta. Visual practice boosts solve rate 2x.

LeetCode 286 Walls and Gates: Why Multi-Source BFS Crushes It—And How One Common Mistake Trips You Up

Grinding LeetCode for Big Tech? Walls and Gates tests your BFS chops hard. This visual breakdown shows the smart path—and one pitfall that burns cycles.

theAIcatchup Apr 09, 2026 3 min read

Step-by-step visual trace of BFS queue expanding from gates in LeetCode 286 grid

⚡ Key Takeaways

Multi-source BFS from all gates hits O(mn) time—ditch per-gate loops. 𝕏
Visual tracers like TraceLit make queue steps intuitive, interview-proof. 𝕏
Common code pitfall: O(mng) waste; fix with single queue and prune checks. 𝕏

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#LeetCode 286 #TraceLit #algorithm visualization #coding interviews #graph algorithms #leetcode-solutions #multi-source BFS #walls-and-gates

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Originally reported by dev.to

⚡ Key Takeaways

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