Sparse array (sparsearray)

Sparse array (sparsearray)

A look at the actual demand

331 procedures written, there are functions to save and exit and continued on disk.

analyse problem:

Because a lot of the value of the two-dimensional array is the default value 0, and therefore makes no sense to record a lot of data .-> sparse array.

basic introduction

• When most of the elements in an array is 0, or a value of the same array, the sparse array can be used to hold the array.

Sparse array of treatment methods are:

1. An array of records, a total of several odd row, how many different values
2. And the ranks of the value of records with different values ​​of the elements in an array of small-scale, thereby reducing the size of the program

Illustrates the sparse array

The first line sparse array value: display original two-dimensional array has several odd row several valid value!

Then one by one began to record where the rms value of the ranks!

Conversion of two-dimensional arrays and sparse arrays

Example: FIG.

Two-dimensional array to a sparse array of ideas:

1. Traversing the original two-dimensional array, the number of valid data obtained sum
2. The sum can create a sparse array sparseArr int [sum + 1] [3]
3. The two-dimensional array of valid data stored in the sparse array

Sparse array to a two-dimensional array of ideas:

1. First reads the first row of the sparse array, according to the data of the first row, to create the original two-dimensional array, such as the above chessArr2 = int [11] [11]
2. And then read a few lines of the sparse array, and assigned to the original two-dimensional array can be!

Code:

package com.atguigu.sparsearray; 

public class SparseArray {
		public static void main(String[] args) {
      // 创建一个原始的二维数组 11 * 11
      // 0: 表示没有棋子， 1：表示黑子 2：表示蓝子 
      int chessArr1[][] = new int[11][11]; 
      chessArr1[1][2] = 1;
      chessArr1[2][3] = 2;
      chessArr1[4][5] = 2;
      // 输出原始的二维数组 
      System.out.println("原始的二维数组~~"); 
      for (int[] row : chessArr1) {
          for (int data : row) {
            System.out.printf("%d\t", data);
          }
          System.out.println();
      }
      // 将二维数组转稀疏数组的思路
      // 1. 先遍历二维数组 得到非 0 数据的个数 
      int sum = 0;
        for (int i = 0; i < 11; i++) {
            for (int j = 0; j < 11; j++) {
            if (chessArr1[i][j] != 0) {
            sum++; 
            }
            }
        }
  // 遍历二维数组，将非 0 的值存放到 sparseArr 中 
      int count = 0;   //count 用于记录是第几个非 0 数据 
      for (int i = 0; i < 11; i++) {
          for (int j = 0; j < 11; j++) {
            if (chessArr1[i][j] != 0) {
            count++;
            sparseArr[count][0] = i;
            sparseArr[count][1] = j;
            sparseArr[count][2] = chessArr1[i][j];
          } 
          }
      }
          // 2. 创建对应的稀疏数组
          int sparseArr[][] = new int[sum + 1][3]; // 给稀疏数组赋值
          sparseArr[0][0] = 11;
          sparseArr[0][1] = 11;
          sparseArr[0][2] = sum;

      // 输出稀疏数组的形式
            System.out.println(); 
      System.out.println("得到稀疏数组为~~~~"); 
      for (int i = 0; i < sparseArr.length; i++) {
        System.out.printf("%d\t%d\t%d\t\n", sparseArr[i][0], sparseArr[i][1], sparseArr[i][2]); 
      }
      System.out.println();

      //将稀疏数组 --》 恢复成 原始的二维数组
      /*
      * 1. 先读取稀疏数组的第一行，根据第一行的数据，创建原始的二维数组，比如上面的chessArr2 = int[11][11]
        2. 在读取稀疏数组后几行的数据，并赋给 原始的二维数组 即可. */

      //1. 先读取稀疏数组的第一行，根据第一行的数据，创建原始的二维数组
      int chessArr2[][] = new int[sparseArr[0][0]][sparseArr[0][1]];
      //2. 在读取稀疏数组后几行的数据(从第二行开始)，并赋给 原始的二维数组 即可
      for(int i = 1; i < sparseArr.length; i++) { 
        chessArr2[sparseArr[i][0]][sparseArr[i][1]] = sparseArr[i][2];
      }
      // 输出恢复后的二维数组 System.out.println(); System.out.println("恢复后的二维数组");
      for (int[] row : chessArr2) { 
        for (int data : row) {
          System.out.printf("%d\t", data);
        }
          System.out.println();
      }
      } 
}