class Solution:
    def solve(self, board: List[List[str]]) -> None:
        """
        Do not return anything, modify board in-place instead.
        """
        que = []
        front = -1
        tail = -1

        def push_back(que, front, tail, ele):
            lq = len(que)
            tail += 1
            if lq <= tail:
                que.append(ele)
            else:
                que[tail] = ele
            return tail
        def pop(que, front, tail):
            front += 1
            return (que[front], front)
        d = [(1,0),(-1,0),(0,1),(0,-1)]
        height = len(board)
        width = len(board[0])
        def is_valid(x, y):
            if x<0 or y < 0 or x >= height or y >= width:
                return False
            return True
        is_visited = []
        for x, l in enumerate(board):
            is_visited.append([])
            for y in l:
                is_visited[x].append(0)
        if height < 3 or width < 3:
            return board
        def is_edge(x, y):
            if x == 0 or y == 0 or x == height - 1 or y == width - 1:
                return True
            return False
        for x in range(1,height - 1):
            for y in range(1,width - 1):
                if board[x][y] == 'X' or is_visited[x][y] == 1: continue
                tail = push_back(que,front, tail,(x,y))
                flag = 0
                last_front = front
                while front != tail:
                    (top_ele, front) = pop(que, front, tail)
                    for (cx, cy) in d:
                        nx = cx + top_ele[0]
                        ny = cy + top_ele[1]
                        if is_edge(nx, ny):
                            if board[nx][ny] == 'O': 
                                flag = 1
                            continue
                        if board[nx][ny] == 'O' and is_visited[nx][ny]==0:
                            tail = push_back(que,front,tail,(nx,ny))
                            is_visited[nx][ny]=1
                if flag == 0:
                    for idx in range(last_front + 1, front + 1):
                        xx = que[idx][0]
                        yy = que[idx][1]
                        board[xx][yy]='X'
        return board