最大岛屿体积，图的用法

public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int num1 = scanner.nextInt();
        int num2 = scanner.nextInt();
        int[][] arr = new int[num1][num2];
        while (scanner.hasNext()){
            for (int i = 0; i < num1; i++) {
                for (int j = 0; j < num2; j++) {
                    arr[i][j] = scanner.nextInt();
                }
            }
            int max = 0;
            for (int i = 0; i < arr.length; i++) {
                for (int j = 0; j < arr[i].length; j++) {
                    if(arr[i][j] > 0){
                        int val = dfs(i,j,arr);
                        max = Math.max(max,val);
                    }
                }
            }
            System.out.println(max);
        }

    }

    private static int dfs(int i, int j,int[][] arr) {
        int res =0;
        if(i < 0 || i >= arr.length || j < 0 || j >= arr[0].length || arr[i][j] == 0){
            return 0;
        }
        res += arr[i][j];
        arr[i][j] = 0;
        res += dfs(i-1,j,arr);
        res +=dfs(i+1,j,arr);
        res +=dfs(i,j+1,arr);
        res +=dfs(i,j-1,arr);
        return res;

    }