02 Sparse array of data structure and algorithm

Introduction

当一个数组中大部分元素为0，或者为同一个值时，可以用稀疏数组来保存该数组

Sparse array processing method

1. 记录数组中一共有几行几列，有多少个不同的值
2. 把具有不同值的元素的行、列及值记录在一个小规模的数组中，从而缩小程序的规模。

Two-dimensional array:

converted sparse array:

Description: How many rows, columns, and valid values ​​are stored in the first row of the array. All subsequent rows record the row number and column number of the valid value respectively.

Code

• Convert a two-dimensional array to a sparse array
  1. Traverse the original two-dimensional array to get the number of valid data sum
  2. According to the sum, you can create a sparse array sparseArr int[sum + 1][3]
  3. Convert the two-dimensional array Valid data is stored in sparse array

  	//创建一个原始的二维数组 11*11
      //0：没有棋子  1：黑子  2：蓝子
      int[][] chessArr1 = new int[11][11];
      for(int i = 0; i<chessArr1.length; i++){
        
        
          for(int j = 0; j<chessArr1[i].length; j++)
              chessArr1[i][j] = 0;
      }
      chessArr1[1][2] = 1;
      chessArr1[2][3] = 2;
      
  	//将二维数组转稀疏数组
      //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 < chessArr1.length; i++){
        
        
          for(int j = 0; j < chessArr1[i].length; j++){
        
        
              if(chessArr1[i][j] != 0)
                  sum++;
          }
      }
  
      //2、创建稀疏数组
      int sparseArr[][] = new int[sum + 1][3];
      //给稀疏数组赋值
      sparseArr[0][0] = chessArr1.length;
      sparseArr[0][1] = chessArr1[0].length;
      sparseArr[0][2] = sum;
      //遍历二维数组，将非0值填入稀疏数组
      int rows = 1;  //记录往稀疏数组的第几行填值
      for(int i = 0; i < chessArr1.length; i++){
        
        
          for(int j = 0; j < chessArr1[i].length; j++){
        
        
              if(chessArr1[i][j] != 0){
        
        
                  sparseArr[rows][0] = i;
                  sparseArr[rows][1] = j;
                  sparseArr[rows++][2] = chessArr1[i][j];
              }
          }
      }
  

• Sparse array is restored to two-dimensional array

  
  //将稀疏数组恢复成二维数组
      int[][] chessArr2 = new int[sparseArr[0][0]][sparseArr[0][1]];
      for(int i = 0; i<sparseArr[0][2]; i++){
        
        
          chessArr2[sparseArr[i+1][0]][sparseArr[i+1][1]] = sparseArr[i+1][2];
      }