Surrounded Regions

MediumAlgorithms

Description

Given an `m x n` board of `'X'` and `'O'`, capture all regions that are 4-directionally surrounded by `'X'`. A region is captured by flipping all `'O'`s into `'X'`s in that region, but only if the region does **not** touch the border. Return the modified board.

Example 1

Input: board = [["X","X","X","X"],["X","O","O","X"],["X","X","O","X"],["X","O","X","X"]]

Output: [["X","X","X","X"],["X","X","X","X"],["X","X","X","X"],["X","O","X","X"]]

Explanation: Only the border-connected O survives.

Constraints

- m == board.length - n == board[i].length - 1 <= m, n <= 200 - board[i][j] is 'X' or 'O'

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