one error in a code maxonebordersize.java

Question

the error ArrayIndexOutOfBoundsException in a loop

public class MaxOneBorderSize {

    public static void setBorderMap(int[][] m, int[][] right, int[][] down) {
       if(m == null){
           return;
       }

   
        right = new int[m.length][m[0].length];
        down  = new  int[m.length][m[0].length];

  
        for(int row = 0; row <m.length;row++ ){
            for(int col = 0; col <m[0].length; col++){
                int index = 0;
                int tempCol = col;


                // 0 - N-1
                while(tempCol<m[0].length && m[row][tempCol] == 1){
                    tempCol++;
                    index++;
                }

                right[row][tempCol-1] = index;
            }
        }


        // 然后生成down的数据

        for(int row = 0; row <m.length;row++ ){
            for(int col = 0; col <m[0].length; col++){
                int index = 0;

                while(row<m.length&&m[row][col] == 1){
                    row++;
                    index++;
                }

                down[row-1][col] = index;
            }
        }
    }



    public static int getMaxSize(int[][] m) {
        int[][] right = new int[m.length][m[0].length];
        int[][] down = new int[m.length][m[0].length];
        setBorderMap(m, right, down); // O(N^2); +

        for (int size = Math.min(m.length, m[0].length); size != 0; size--) {
            if (hasSizeOfBorder(size, right, down)) {
                return size;
            }
        }
        return 0;
    }

    public static boolean hasSizeOfBorder(int size, int[][] right, int[][] down) {
        for (int i = 0; i != right.length - size + 1; i++) {
            for (int j = 0; j != right[0].length - size + 1; j++) {
                if (right[i][j] >= size && down[i][j] >= size
                        && right[i + size - 1][j] >= size
                        && down[i][j + size - 1] >= size) {
                    return true;
                }
            }
        }
        return false;
    }

    public static int[][] generateRandom01Matrix(int rowSize, int colSize) {
        int[][] res = new int[rowSize][colSize];
        for (int i = 0; i != rowSize; i++) {
            for (int j = 0; j != colSize; j++) {
                res[i][j] = (int) (Math.random() * 2);
            }
        }
        return res;
    }

    public static void printMatrix(int[][] matrix) {
        for (int i = 0; i != matrix.length; i++) {
            for (int j = 0; j != matrix[0].length; j++) {
                System.out.print(matrix[i][j] + " ");
            }
            System.out.println();
        }
    }

    public static void main(String[] args) {
        int[][] matrix = generateRandom01Matrix(7, 8);
        printMatrix(matrix);
        System.out.println(getMaxSize(matrix));
    }
}

1 0 0 0 1 0 1 1
1 0 0 1 0 1 1 0
0 0 1 1 0 1 1 0
0 0 0 1 0 0 1 1
1 1 1 0 1 0 0 1
0 0 1 1 1 0 1 0
0 1 0 0 1 1 0 0

I have completed the code to get the longest side of the rectangle consists of ‘1’. But the error java.lang.ArrayIndexOutOfBoundsException has occured in

for(int row = 0; row <m.length;row++ ){
            for(int col = 0; col <m[0].length; col++){
                int index = 0;
                int tempCol = col;


                // 0 - N-1
                while(tempCol<m[0].length && m[row][tempCol] == 1){
                    tempCol++;
                    index++;
                }

                right[row][tempCol-1] = index;
            }
        }

I don't have any idea about that.

Please add the exact and full exception to the question. This should explain what the index was trying to access when it was out of bounds. — NomadMaker, Jun 18 '21 at 23:52

score 1 · Accepted Answer · edited Jun 21 '21 at 12:03

In this line you have not handled exception for the condition tempCol = 0 which would make tempcol = -1 in the code and it will be out of bounds.

right[row][tempCol-1] = index;

There are two ways to handle this either use try catch or if else with proper condition

for(int row = 0; row <m.length;row++ ){
   for(int col = 0; col <m[0].length; col++){
     int index = 0;
     int tempCol = col;

     while(tempCol<m[0].length && m[row][tempCol] == 1){
       tempCol++;
       index++;
     }

     if(tempCol!=0){
       right[row][tempCol-1] = index;
     }
     else{
       right[row][tempCol] = index;
     }

   }
 }

There is same problem with the down array which has row-1.

Also next time posting a question use proper proportionate indentation.

Exception：

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1
    at MaxOneBorderSize.setBorderMap(MaxOneBorderSize.java:25)
    at MaxOneBorderSize.getMaxSize(MaxOneBorderSize.java:51)
    at MaxOneBorderSize.main(MaxOneBorderSize.java:96)

one error in a code maxonebordersize.java

1 Answers1