A confusing exception out of bound error in java while solving a spiral 2d matrix question

Question

I was solving this question, trying to generate spiral matrix but repeatedly getting error only when the length of the matrix is odd. It is working fine when the length is even

This is the code:

public class spiral {
    public static void main(String[] args) {
        int n = 5;
        generateSpiralMat(n);
    }

    static void generateSpiralMat(int n) {
        int[][] mat = new int[n][n] ;
        int topRow =0, rightCol = n-1, bottonRow = n-1, leftCol = 0 ;
        int num = 1 ;

        while( num < n*n + 1 ) {
            //topRow -> leftCol to rightCol
            for(int i=leftCol; i<rightCol; i++) {
                mat[topRow][i] = num;
                num ++ ;
            }

            //rightCol -> topRow to bottomRow
            for(int j =topRow; j<bottonRow; j++){
                mat[j][rightCol] = num ;
                num++ ;
            }

            //bottomRow -> rightCol to leftCol
            for(int i=rightCol; i> leftCol; i--) {
                mat[bottonRow][i] = num;
                num++ ;
            }

            //leftCol -> bottomRow to topRow
            for(int j=bottonRow; j>topRow; j--) {
                mat[j][leftCol] = num ;
                num ++ ;
            }

            topRow += 1 ;
            bottonRow -= 1 ;
            leftCol += 1 ;
            rightCol -= 1 ;
        }

        printMat(mat);
    }

    static void printMat(int[][] mat) {
        for(int i=0; i< mat.length; i++) {
            for(int j=0; j< mat[i].length; j++) {
                System.out.print( mat[i][j] + " ");
            }
            System.out.println();
        }
    }
}

Even length matrix working well but code is showing error in runtime only for odd length matrix

I was expecting that the code would generate a spiral matrix as per the given question.

Answer 1

void spiral( int side ) {
   int matriz[][] = new int[ side ][ side ];
   int length = side * side;
   int count = 0;
   int top = side - 1;
   int floor = 0;
   int sector = 0;
   int j = 0, k = 0;
   for( int i = 0; i < length; i++ ) { 
      matriz[ j ][ k ] = count;
      switch( sector ) {
         case 3: j--;
            if( j == floor ) {
               sector = 0;
               top -= 1;
            }
            break;
         case 2: k--;
            if( k == floor ) {
               floor++;
               sector++;
            }
            break;
         case 1: j++;
            if( j == top ) {
               sector++;
            }
            break;
         case 0: k++;
            if( k == top ) {
               sector++;
            }
            break; 
      }
      count++;
   } 
}

We divide the operation into four stages:
A) advance in the columns
B) advance in the rows
C) back in the columns
D) back in rows
when it reaches the corresponding limit, it goes to the next sector, in sector "3" the upper limit is modified, and in "2" the lower limit.