Capture the Enclosed Outposts

medium

In a territory-control game, the board is a grid of "X" (your walls) and "O" (enemy outposts). At the end of a round, every group of outposts that is fully sealed off — i.e. cannot reach the edge of the board through adjacent outposts — is captured and converted to "X". Outpost groups touching the border survive.

Given the grid board, return the board after all captures. Adjacency is horizontal and vertical only.

Example 1

in board = [["X","X","X"],["X","O","X"],["X","X","X"]]

out [["X","X","X"],["X","X","X"],["X","X","X"]]

The lone central outpost is sealed and captured.

Example 2

in board = [["O","X"],["X","X"]]

out [["O","X"],["X","X"]]

The outpost touches the border, so it survives.

Constraints

· 1 <= rows, cols <= 12
· board[r][c] is "X" or "O"