I have done the same thing in java but my few test cases are showing incorrect. Please help here is the code:

static String[] cavityMap(String[] grid) { for(int i = 1; i < grid[0].length() - 1; i++) { for(int j = 1; j < grid[0].length() - 1; j++) { if(Character.getNumericValue(grid[i].charAt(j)) > Character.getNumericValue(grid[i].charAt(j-1)) && Character.getNumericValue(grid[i].charAt(j)) > Character.getNumericValue(grid[i].charAt(j+1)) && Character.getNumericValue(grid[i].charAt(j)) > Character.getNumericValue(grid[i - 1].charAt(j)) && Character.getNumericValue(grid[i].charAt(j)) > Character.getNumericValue(grid[i + 1].charAt(j))) { grid[i] = grid[i].replace(grid[i].charAt(j), 'X');

            }
        }
    }

    return grid;

}