You are given an m x n matrix board containing letters 'X' and 'O', capture regions that are surrounded:
'O' cell.'X' cells if you can connect the region with 'X' cells and none of the region cells are on the edge of the board.A surrounded region is captured by replacing all 'O's with 'X's in the input matrix 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:
+
+In the above diagram, the bottom region is not captured because it is on the edge of the board and cannot be surrounded.
+Example 2:
+ +Input: board = [["X"]]
+ +Output: [["X"]]
++
Constraints:
+ +m == board.lengthn == board[i].length1 <= m, n <= 200board[i][j] is 'X' or 'O'.