Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

For example, Given n = 3, You should return the following matrix:

[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

Solution:

public class Solution {
    public int[][] generateMatrix(int n) {
        int[][] ans = new int[n][n];
        int[][] dir = new int[][]{{0,1},{1,0},{0,-1},{-1,0}};
        int[] step = new int[]{n,n-1};
        int i=0, j=-1;
        int d=0;
        int num=1;
        while(step[d%2]>0){
            for(int k=0; k<step[d%2]; k++){
                i += dir[d][0];
                j += dir[d][1];
                ans[i][j] = num++;
            }
            step[d%2]--;
            d = (d+1)%4;
        }
        return ans;
    }
}