Mutual transformation between two-dimensional array and sparse array (sparse matrix)

What is a sparse array , Look at the picture

Convert to sparse array

The following code is used to realize the mutual transformation of array and sparse array （ Dynamic , You can modify the storage elements of the original array at will ）：

public class day1Test01 {
    
    public static void main(String[] args) {
    
        int[][] arr = new int[6][6];
        int sum = 0;
        arr[0][0] = 1;
        arr[1][1] =2;
        arr[3][3]=4;
        arr[2][1]=3;
        for (int i = 0; i < arr.length; i++) {
    
            for (int j = 0; j < arr[0].length; j++) {
    
                if ((arr[i][j]) != 0) {
    
                    sum = sum + 1;
                }
                System.out.printf("%d\t",arr[i][j]);
            }
            System.out.println();
        }
        //======================================================================
        System.out.println(" The two-dimensional array is converted into a sparse array and the conversion begins ");
        int[][] xishuarr = new int[sum + 1][3];
        xishuarr[0][0] = arr.length;
        xishuarr[0][1] = arr[0].length;
        xishuarr[0][2] = sum;
        int a=0;
            for (int i = 0; i < arr.length; i++) {
    
                for (int j = 0; j < arr[0].length; j++) {
    
                    if ((arr[i][j]) != 0) {
    
                             a=a+1;
                            xishuarr[a][2] = arr[i][j];
                            xishuarr[a][0] = i;
                            xishuarr[a][1] = j;
                    }
                }
            }

            for (int m = 0; m < xishuarr.length; m++) {
    
                for (int n = 0; n < xishuarr[0].length; n++) {
    
                    System.out.printf("%d\t",xishuarr[m][n]);
                }
                System.out.println();
            }
        // Convert sparse array to two-dimensional array 
        System.out.println(" Sparse arrays begin to be converted into two-dimensional arrays ");
        int arr2[][]=new int [xishuarr[0][0]][xishuarr[0][1]];
            int resum=xishuarr[0][2];
            for (int i=0;i<resum;i++){
    
                arr2[xishuarr[i+1][0]][xishuarr[i+1][1]]=xishuarr[i+1][2];
            }
            for (int [] row :arr2){
    
                for (int data:row){
    
                    System.out.printf("%d\t",data);
                }
                System.out.println();
            }
        }
    }
    ** Output is as follows **
 Two dimensional array traversal results ：
1	0	0	0	0	0	
0	2	0	0	0	0	
0	3	0	0	0	0	
0	0	0	4	0	0	
0	0	0	0	0	0	
0	0	0	0	0	0	
 The two-dimensional array is converted into a sparse array and the conversion begins 
6	6	4	
0	0	1	
1	1	2	
2	1	3	
3	3	4	
 Sparse arrays begin to be converted into two-dimensional arrays 
1	0	0	0	0	0	
0	2	0	0	0	0	
0	3	0	0	0	0	
0	0	0	4	0	0	
0	0	0	0	0	0	
0	0	0	0	0	0