sorting array of arrays in descending order using arrays.sort function is resulting in errors in java

Question

problem: https://leetcode.com/problems/maximum-units-on-a-truck/ I am supposed to sort array of arrays of size 2(eg. [[1,3],[2,2],[3,1]]) in descending order according to 2nd value of the inner element. ie for 1st element[1,3]according to value 3. , but my code is resulting in error: no suitable method found for sort().Some Help would be appreciated.

here is my code in java

class Solution {
    public int maximumUnits(int[][] boxTypes, int truckSize) {
        Arrays.sort(boxTypes, new Comparator<int[][]>() {
                    public int compare(final int[][] entry1, final int[][] entry2) {
                        if (entry1[0][0] < entry2[0][0])
                            return 1;
                        else return -1;
                    }
                }
        );
        for (int i = 0; i < boxTypes.length; i++)
            System.out.println(boxTypes[i]);
        return 0;
    }
}

Answer 1

As mentioned in comments, you are sorting by inner element, which is int[] , so you need Comparator<int[]> .

public class Solution {

    public static void main(String[] args) {
        int[][] input = new int[][]{new int[]{2, 2}, new int[]{1, 3}, new int[]{3, 1}};
        Arrays.sort(input, new Comparator<int[]>() {

            @Override
            public int compare(int[] o1, int[] o2) {
                return Integer.compare(o2[1], o1[1]);
            }
        });
        System.out.println(Arrays.deepToString(input));
    }
}

Note return Integer.compare(o2[1], o1[1]); , second parameter is compared to first in order to achieve descending order.

You could also achieve same effect using lambda, to make it shorter and more readable.

public class Solution {

    public static void main(String[] args) {
        int[][] input = new int[][]{new int[]{2, 2}, new int[]{1, 3}, new int[]{3, 1}};
        System.out.println("Initial array - " + Arrays.deepToString(input));
        Arrays.sort(input, (o1, o2) -> Integer.compare(o2[1], o1[1]));
        System.out.println("Sorted array - " + Arrays.deepToString(input));
    }
}

Answer 2

First, you can't use native type in <> , you need to use Integer instead. Then what you need to compare is the inner array Integer[] if I'm not mistaken so your comparator can't work. Here you are just trying to sort 2 arrays of arrays based on the first element of the first array.

Here is what I would do (using stream):

Integer[][] sortedBoxTypes = Arrays.stream(boxTypes).sorted(Comparator.comparing(entry -> entry[1])).toArray(Integer[][]::new);