Sparse Array

Recognition: When most elements in an array are 0 or the same data, a sparse array can be used to store its effective information.

Purpose: To reduce waste of storage space, compress data size, and save only useful information

Storage method:

Stored in a two-dimensional array, in a sparse array

6 Represented by a sparse array: arr [0] [0];

7 Represented by a sparse array: arr [0] [1];

8 Represented by a sparse array: arr [0] [2];

 

5 Represented by a sparse array: arr [8] [0];

2 Represented by a sparse array: arr [8] [1];

28 Represented by a sparse array: arr [8] [2];

 

Schematic representation of multi-dimensional array:

 

 

Schematic diagram of converting a two-dimensional matrix into a sparse array:

package array;
public class ArrayDemo06 {

public static void main(String[] args) {

int[][] arr1 = new int[5][5];

arr1[1][2] = 1;

arr1[2][3] = 2;

System.out.println("原始二维数组：");

for (int[] ints : arr1) {

for (int anInt : ints) {

System.out.print(anInt+"\t");

}

System.out.println();

}

/*

变为稀疏数组

*/
   //获取有用数据的个数
    int sum = 0;
    for (int i = 0; i < arr1.length; i++) {
        for (int j = 0; j < arr1[i].length; j++) {
            if(arr1[i][j] != 0){
                sum++;
            }
        }
    }
    //获取数组总共有几行、几列（arr1.length,arr1[0].length）
    //构建稀疏数组

    int[][] arr2 = new int[sum+1][3];
    arr2[0][0] = arr1.length;
    arr2[0][1] = arr1[0].length;
    arr2[0][2] = sum;

    //获取有用数据的行、列、值,赋值稀疏矩阵
    int num=0;
    for (int i = 0; i < arr1.length; i++) {
        for (int j = 0; j < arr1.length; j++) {
            if(arr1[i][j] != 0){
                num++;
                arr2[num][0] = i;
                arr2[num][1] = j;
                arr2[num][2] =arr1[i][j];
            }
        }
    }

    //稀疏数组的输出
    System.out.println("稀疏数组的输出：");
    for (int[] ints : arr2) {
        for (int anInt : ints) {
            System.out.print(anInt+"\t");
        }
        System.out.println();
    }


    /*
    稀疏数组还原为二维数组
     */
    //二维数组赋值
    int[][] arr3 = new int[arr2[0][0]][arr2[0][1]];
    for (int i = 1; i < arr2.length; i++) {
        arr3[arr2[i][0]][arr2[i][1]] = arr2[i][2];
    }

    //二维数组输出
    System.out.println("还原数组输出：");
    for (int[] ints : arr3) {
        for (int anInt : ints) {
            System.out.print(anInt+"\t");
        }
        System.out.println();
    }
}

}

 

原始二维数组：
0	0	0	0	0	
0	0	1	0	0	
0	0	0	2	0	
0	0	0	0	0	
0	0	0	0	0	
稀疏数组的输出：
5	5	2	
1	2	1	
2	3	2	
还原数组输出：
0	0	0	0	0	
0	0	1	0	0	
0	0	0	2	0	
0	0	0	0	0	
0	0	0	0	0