Surrounded Regions
Given a matrix of 'X' and 'O' characters Capture (flip to 'X') all regions that are completely surrounded by 'X' A region is NOT surrounded if it touches the border Return the modified board Example: [["X","X","X"],["X","O","X"],["X","X","X"]] => [["X","X","X"],["X","X","X"],["X","X","X"]]
Surrounded Regions is a traversal problem: the hard part is modeling the state you visit. Interviewers love it because it reveals your traversal modeling and your edge-case discipline. Once your traversal structure is solid, you can reuse it across dozens of problems.
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