在大型 7*7 矩阵中遍历 3* 3 子矩阵时边界异常错误的数组索引

Question

我想在从中间元素(第 2 行、第 2 列(开始的 7*7 大矩阵起始位置内遍历一个 3*3 子矩阵。 位置 (1,1( 的相应子矩阵为

[(0,1),(0,2),(0,3)]
[(1,1),(1,2),(1,3)]
[(2,1),(2,2),(2,3)]

像这样遍历将继续..下一个子矩阵起始位置将是(1,2(

[(0,2),(0,3),(0,4)]
[(1,2),(1,3),(1,4)]
[(2,2),(2,3),(2,4)]

我的代码

static int i;
static int j;
static int g;
static int h;
static void submatrix(int p,int q,int[][] mat) {
System.out.print("Submatrix for : ");
System.out.println(p+","+q);
shiftmatrix(p,q,mat);
}
static void shiftmatrix(int p,int q,int[][] mat) {
int m,n;
int[][] d = new int[3][3];
for( m=0;m<3;m++) {
for( n=0;n<3;n++) {
p=m+(p-1);
q=n+q;
d[m][n]=mat[p][q];
}
}
System.out.println("Your 3*3 SubMatrix is : ");
for ( m = 0; m < 3; m++){
for ( n = 0; n < 3; n++){
System.out.print(d[m][n]+"t");
}
System.out.println();
}
}
public static void main(String[] args) {
int[][] a = new int[7][7];
int[][] mat = new int[7][7];
for ( i = 0; i < 7; i++)
{
for ( j = 0; j < 7; j++){
Random rand = new Random();
a[i][j] = rand.nextInt(10);
}
}
//copying large matrix to another for passing by argument 
System.out.println("Copied matrix is : ");
for (i = 0; i < 7; i++){
for (j = 0; j < 7; j++){
mat[g][h]=a[i][j];
System.out.print(mat[g][h]+"t");
}
System.out.println();
}
//Here is the 3*3 submatrix traversing starts...
for (i=1;i<6;i++) {
for (j=1;j<5;j++) {
int p=i;
int q=j;
submatrix(p,q,mat);
}
}
}
}

运行此代码时出现错误

ArrayIndexOutOfBoundsException: -1 

请帮忙

Answer 1

代码中的IndexOutOfBoundsException来自您调用p = m + (p - 1)。您无需在循环的每次迭代中更改p和q变量。

此外，您有几个不必要的变量，其中一些是静态的，当您仅在这样的循环中使用它们时，您应该避免这种情况。在清理代码的格式并删除所有不必要的变量后，我相信代码可以按照您想要的方式运行。

代码忽略随机矩阵的第一行和第一列。这是期望的行为吗？

import java.util.Random;
public class MatrixTest {
public static void subMatrix(int startRow, int startCol, int[][] mat) {
System.out.print("Submatrix for : ");
System.out.println(startRow + ", " + startCol);
shiftMatrix(startRow, startCol, mat);
}
public static void shiftMatrix(int startRow, int startCol, int[][] mat) {
int[][] d = new int[3][3];
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
//to properly move within the 3x3 you only need to add a 
//constant buffer to the indices of mat[][]
d[i][j] = mat[i + startRow][j + startCol]; 
}
}
System.out.println("Your 3*3 SubMatrix is : ");
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
System.out.print(d[i][j] + "t");
}
System.out.println();
}
}
public static void main(String[] args) {
int[][] mat = new int[7][7];
for (int i = 0; i < 7; i++) {
for (int j = 0; j < 7; j++){
Random rand = new Random();
mat[i][j] = rand.nextInt(10);
}
}
//copying large matrix to another for passing by argument 
System.out.println("Copied matrix is : ");
for (int i = 0; i < 7; i++){
for (int j = 0; j < 7; j++) {
System.out.print(mat[i][j] + "t");
}
System.out.println();
}
//Here is the 3*3 submatrix traversing starts...
for (int i = 1; i < 5; i++) { //changed from i < 6 to i < 5 to stay inside 7x7
for (int j = 1; j < 5; j++) {
subMatrix(i, j, mat);
}
}
}
}