二维数组与稀疏数组的互转

​​当二维数组中有大量的0时,可以用稀疏数组对二位数组进行压缩存储,稀疏数组可以大大的节省存储空间​​

如:
​​​普通二维数组​​

0   0   0   0   0   0   0   0   0   0   0   
0   0   0   0   0   0   0   0   0   0   0   
0   0   0   1   0   0   0   0   0   0   0   
0   0   0   0   2   0   0   0   0   0   0   
0   0   0   0   0   0   0   0   0   0   0   
0   0   0   0   0   0   0   0   0   0   0   
0   0   0   0   0   0   0   0   0   0   0   
0   0   0   0   0   0   0   0   0   0   0   
0   0   0   0   0   0   0   0   0   1   0   
0   0   0   0   0   0   0   0   0   0   0   
0   0   0   0   0   0   0   0   0   0   0

​​转为稀疏数组时​​

11  11  3   
2   3   1   
3   4   2   
8   9   1

​​稀疏数组的格式​​

二维数组的行数 二维数组的列数 非零元素的个数
  行坐标         列坐标         值
  行坐标         列坐标         值
  行坐标         列坐标         值
       ......
  行坐标         列坐标         值

将二维数组转为稀疏数组并存储到文件中
将文件中存储的稀疏数组取出来，再转换为二维数组

package com.whb.sparsearray;

import java.io.*;

public class SparseArray {


    public static void main(String[] args) {

        int[][] arr = new int[11][11];

        arr[2][3] = 1;
        arr[3][4] = 2;
        arr[8][9] = 1;

        for (int i=0; i < arr.length; i++){
            for (int j=0; j < arr[0].length; j++){

                System.out.printf("%d\t",arr[i][j]);
            }
            System.out.println();
        }

        int sum = 0;

        for (int i = 0; i < 11; i++) {

            for (int j = 0; j < 11; j++) {

                if(arr[i][j]!=0){
                    sum++;
                }
            }

        }

        /**
         * 矩阵转稀疏数组
         */
        int[][] sparseArr = new int[sum+1][3];
        sparseArr[0][0] = arr.length;
        sparseArr[0][1] = arr[0].length;
        sparseArr[0][2] = sum;

        int count = 1;

        for (int i = 0; i < 11; i++) {
            for (int j = 0; j < 11; j++) {
                if(arr[i][j]!=0){
                    sparseArr[count][0] = i;
                    sparseArr[count][1] = j;
                    sparseArr[count][2] = arr[i][j];
                    count++;
                }
            }
        }

        System.out.println();

//        for (int i = 0; i < sparseArr.length; i++) {
//            for (int j = 0; j < sparseArr[0].length; j++) {
//                System.out.printf("%d\t",sparseArr[i][j]);
//            }
//            System.out.println();
//        }
//        System.out.println();

        // 写入
        try {
            BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("./data.txt")));
            for (int i = 0; i < sparseArr.length; i++) {
                for (int j = 0; j < sparseArr[i].length; j++) {
                    if(j!=sparseArr[i].length-1){
                        bw.write(sparseArr[i][j]+" ");
                    }else{
                        bw.write(sparseArr[i][j]+"");
                    }
                }
                if(i!=sparseArr.length-1){

                    bw.newLine();
                }
            }
            bw.flush();
        } catch (Exception e) {

        }

        int[][] readarr = null;
        //读取
        try {
            BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("./data.txt")));
            String firstLine = br.readLine();
            String[] sarr = firstLine.split(" ");

            readarr = new int[Integer.parseInt(sarr[0])][Integer.parseInt(sarr[1])];

            String s = null;
            while ((s = br.readLine())!=null){
                sarr = s.split(" ");
                readarr[Integer.parseInt(sarr[0])][Integer.parseInt(sarr[1])] = Integer.parseInt(sarr[2]);
            }

        } catch (Exception e) {

        }
        System.out.println("开始打印");

        for (int i = 0; i < readarr.length; i++) {
            for (int j = 0; j < readarr[0].length; j++) {
                System.out.printf("%d\t",readarr[i][j]);
            }
            System.out.println();
        }


//        /**
//         * 稀疏数组转矩阵
//         */
//
//        int[][] newArr = new int[sparseArr[0][0]][sparseArr[0][1]];
//        for (int i = 1; i < sparseArr.length; i++) {
//
//            newArr[sparseArr[i][0]][sparseArr[i][1]] = sparseArr[i][2];
//
//        }
//
//
//        for (int i = 0; i < newArr.length; i++) {
//            for (int j = 0; j < newArr[0].length; j++) {
//                System.out.printf("%d\t",newArr[i][j]);
//            }
//            System.out.println();
//        }
    }

}