130. Surrounded Regions - LeetCode Solution

class Solution:
    def solve(self, board: List[List[str]]) -> None:
        def Erase(rid, cid):
            if rid < 0 or cid < 0 or rid > len(board) -1 or cid > len(board[0]) -1 or board[rid][cid] in ('X', 'E'):
                return
            board[rid][cid] = 'E'
            Erase(rid-1, cid)
            Erase(rid+1, cid)
            Erase(rid, cid-1)
            Erase(rid, cid+1)
            
            
        for rid, row in enumerate(board):
            for cid, column in enumerate(row):
                if rid == 0 or cid == 0 or rid == len(board) -1 or cid == len(board[0])-1:
                    if board[rid][cid] == 'O':
                        Erase(rid, cid)
    
        for rid, row in enumerate(board):
            for cid, column in enumerate(row):
                if board[rid][cid] == 'O':
                    board[rid][cid] = 'X'
                if board[rid][cid] == 'E':
                    board[rid][cid] = 'O'