LeetCode 130: Surrounded Regions — Step-by-Step Visual Trace

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Learn to solve LeetCode 130 by identifying and capturing surrounded regions of 'O' in a 2D board

intermediate Published 9 Apr 2026

Action Steps

Create a 2D board with 'X' and 'O' regions
Identify the regions connected to the border using Depth-First Search (DFS)
Mark the identified regions as 'N' to distinguish them from surrounded regions
Iterate through the board to capture surrounded 'O' regions by flipping them to 'X'
Replace the 'N' marks with 'O' to restore the original border-connected regions

Who Needs to Know This

Software engineers and developers can benefit from this lesson to improve their problem-solving skills and algorithmic thinking

Key Insight

💡 Use DFS to identify border-connected regions and avoid capturing them

Key Takeaways

Learn to solve LeetCode 130 by identifying and capturing surrounded regions of 'O' in a 2D board

Full Article

Given a 2D board containing ''X'' and ''O'', capture all regions of ''O'' that are completely surrounded by ''X'' by flipping them to ''X''. Regions connected to the border cannot be captured.

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