vector<string> cavityMap(vector<string> &grid) {
    for (int i = 1; i < grid.size() - 1; i++) {
        for (int j = 1; j < grid[i].length() - 1; j++) {
            if (grid[i][j] > grid[i][j - 1] && grid[i][j] > grid[i][j + 1]) {
                if(grid[i][j] > grid[i-1][j] && grid[i][j] > grid[i+1][j]) {
                    grid[i][j] = 'X';
                }
            }
        }
    }
    return grid;
}