LeetCode 130: Surrounded Regions — Step-by-Step...

Medium — Depth-First Search | Matrix | Graph Traversal | Flood Fill The Problem 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. Approach Use DFS to mark all 'O' cells connected to the border as 'E' (escaped). Then traverse the entire board: flip remaining 'O' cells to 'X' (captured) and restore 'E' cells back to 'O' (escaped). This reverse approach identifies unc