What is the time complexity of LeetCode 130 solution?

O(m*n). Single pass marks, single pass flips.

How to avoid recursion depth issues in Surrounded Regions?

Use iterative DFS or BFS with stack/queue. Swap recursion for loop.

What makes TraceLit better for LeetCode practice?

Visual line-by-line traces. See data flow, no brain-melt.

LeetCode 130: Why Reversing the DFS Flood Fill Actually Crushes It

Everyone dives into every 'O', hunting borders. Wrong move. Flip the script—start from edges. TraceLit visualizes why this DFS hack owns LeetCode 130.

theAIcatchup Apr 09, 2026 3 min read

Step-by-step visual trace of LeetCode 130 board with DFS flood fill from borders

⚡ Key Takeaways

Reverse DFS from borders marks escapees first — O(m*n) win. 𝕏
TraceLit visualizes recursion, slashing debug frustration. 𝕏
LeetCode matrices are graph traversal; master one, own 'em all. 𝕏

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theAIcatchup

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#DFS #Flood Fill #LeetCode 130 #Surrounded Regions #TraceLit #algorithm visualization

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Originally reported by dev.to

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