public class SpareMatrix {
    public static void main(String[] args) {
        int[][] arrs = new int[5][5];
        arrs[1][1] = 1;
        arrs[1][2] = 2;
        arrs[2][3] = 1;
        System.out.print(ArraytoString(arrs));
        arrs=convertToSpareMatrix(arrs);
        System.out.print(ArraytoString(arrs));
        arrs = convertToArray(arrs);
        System.out.print(ArraytoString(arrs));
    }
    //转换稀疏矩阵
    private static int[][] convertToSpareMatrix(int[][] ars) {
        // TODO 自动生成的方法存根
        //计算非0值的数量
        int noZeroSum = 0;
        for (int[] rows : ars) {
            for (int num : rows) {
                if (num!=0) {
                    noZeroSum++;
                };
            }
        }
        //创建空数组
        int[][] spArr = new int[noZeroSum+1][3];
        spArr[0][0]=ars.length;
        spArr[0][1]=ars[0].length;
        spArr[0][2]=noZeroSum;
        int index = 1;
        //遍历原数组的有效元素
        for (int i = 0; i < ars.length; i++) {
            for (int j = 0; j < ars[i].length; j++) {
                int tmp = ars[i][j];
                if(tmp!=0) {
                    spArr[index][0]=i;
                    spArr[index][1]=j;
                    spArr[index][2]=tmp;
                    index++;
                }
            }
        }
        return spArr;
    }
    //稀疏矩阵转换回数组
    private static int[][] convertToArray(int[][] ars) {
        // TODO 自动生成的方法存根
        int[][] nmArr = new int[ars[0][0]][ars[0][1]];
        for (int i = 1; i < ars.length; i++) {
            nmArr[ars[i][0]][ars[i][1]]=ars[i][2];
        }

        return nmArr;
    }   
    //打印数组
    public static String ArraytoString(int[][] ars) {
        StringBuilder stringBuilder = new StringBuilder();
        for (int[] rows : ars) {
            for (int num : rows) {
                stringBuilder.append(num);
            }
            stringBuilder.append("\r\n");
        }
        return stringBuilder.toString();
    }
}