查找相邻矩阵：Java.lang.ArrayIndexOutOfBoundsException

Question

我正在尝试查找矩阵中的所有相邻元素。相邻是指水平、垂直和对角线元素彼此相邻的元素。但是它给了我java.lang.ArrayIndexOutOfBoundsException: Index 5 out of bounds for length 5。我不知道为什么，任何帮助将不胜感激！程序也需要递归！

class matrixAdjacent
{
   public static void main(String[] args) 
   {
      char grid[][] = {{'0','0','0','1','1','0','1','1','0','0','0','1','1','1','0','1','1','1','0','1'},
                      {'1','0','0','0','0','1','0','0','0','1','0','0','0','0','0','1','1','1','1','1'},
                      {'0','1','0','0','1','0','0','0','1','0','1','0','0','0','0','0','0','1','1','1'},
                      {'1','1','1','0','0','1','0','1','0','0','0','0','1','0','1','1','0','1','1','0'},
                      {'0','1','1','1','0','1','1','1','0','1','0','0','1','0','1','0','1','1','0','1'}};
      
      ExploreAndLabelColony(grid, 0, 0);
   }


private static void ExploreAndLabelColony(char[][] grid, int i, int j) 
{
    // TODO Auto-generated method stub
    if(grid==null)
    {
        return;
    }
    if(i==grid.length || j==grid[0].length) 
    {
        return;
    }  
    
    if (grid[i][j] == '1') //checks if theres a 1 which refers to a colony      
    {
      if (i>0 && i + 1 < grid.length && j>0 && j + 1 < grid[0].length) 
      {
         if (grid[i+1]==grid[j] || grid[i] == grid[j+1] || grid[i-1]==grid[j] || grid[i]==grid[j-1]) //checks if adjacent
         {
           grid[i][j] = 'A'; //creates a colony
         }
      }
    }
    else if(grid[i][j] == '0') //replaces 0 with '-'
    {
      grid[i][j] = '-';  
    }
    
    System.out.print(grid[i][j]); //print grid
    if(j==grid[0].length-1)
    {
      System.out.println();      //prints next row
      ExploreAndLabelColony(grid,i+1,0); //recurse to increment row 
    }     
    ExploreAndLabelColony(grid,i,j+1); //recurse to increment column
      
    }
}

Answer 1

问题

      if (i>0 && i + 1 < grid.length && j>0 && j + 1 < grid[0].length) 
      {
         if (grid[i+1]==grid[j] || grid[i] == grid[j+1] || grid[i-1]==grid[j] || grid[i]==grid[j-1]) //checks if adjacent
         {
           grid[i][j] = 'A'; //creates a colony
         }
      }

在上面这段代码中，j>0 && j + 1 < grid[0].length不能保证对grid[j]的访问。

对内部数组索引的检查无法正确验证对外部数组索引的访问。

检查相邻元素

要检查相邻元素，必须检查所有 4 个有效的相邻索引

1. grid[i][j - 1]
2. grid[i][j + 1]
3. grid[i - 1][j]
4. grid[i + 1][j]

在上述 4 项检查中，请在进行 i - 1、i + 1、j - 1、j + 1 访问之前验证索引。

Answer 2

对于坐标为i、j的给定单元格，相邻元素位于正方形中：

[i - 1][j - 1], [i - 1][j], [i - 1][j + 1]
[i    ][j - 1],  CURR_CELL, [i    ][j + 1]
[i + 1][j - 1], [i + 1][j], [i + 1][j + 1]

可以使用Math.min、Math.max 函数应用其他限制，并且可以按如下方式检测相邻单元格：

if (grid[i][j] == '1') {  //checks if theres a 1 which refers to a colony
    out: // label to break
    for (int ii = Math.max(i - 1, 0), in = Math.min(grid.length, i + 2); ii < in; ii++) {
        for (int jj = Math.max(j - 1, 0), jn = Math.min(grid[0].length, j + 2); jj < jn; jj++) {
            if (ii == i && jj == j) {
                continue; // skip reference cell
            }
            if (grid[ii][jj] == '1') {
                grid[i][j] = 'A';
                break out; // as soon as the first neighbor is found
            }
        }
    }
}

通过此更改，给定输入的输出：

public static void main(String[] args) {
    char grid[][] = {
        {'0','0','0','1','1','0','1','1','0','0','0','1','1','1','0','1','1','1','0','1'},
        {'1','0','0','0','0','1','0','0','0','1','0','0','0','0','0','1','1','1','1','1'},
        {'0','1','0','0','1','0','0','0','1','0','1','0','0','0','0','0','0','1','1','1'},
        {'1','1','1','0','0','1','0','1','0','0','0','0','1','0','1','1','0','1','1','0'},
        {'0','1','1','1','0','1','1','1','0','1','0','0','1','0','1','0','1','1','0','1'}
    };
      
    ExploreAndLabelColony(grid, 0, 0);
}

如下：

---AA-A1---AA1-AAA-A
A----A---A-----AAAAA
-A--A---A-1------AAA
AAA--A-A----A-AA-AA-
-AA1-AA1-1--1-1-A1-1

可能，应修复条件以检查相邻单元格是否已包含A，或者是否有太多邻居但设置/应用这些或任何其他规则取决于作者。