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 ]]

public class Solution {    public int[][] generateMatrix(int n) {        int [][]a=new int[n][n];                int val=0;        for(int layer=0;layer<n/2;++layer){            int first=layer;            int last=n-1-layer;            for(int i=first;i<last;++i){                val++;                a[first][i]=val;            }            for(int j=first;j<last;j++){                val++;                a[j][last]=val;            }            for(int k=last;k>first;k--){                val++;                a[last][k]=val;            }            for(int l=last;l>layer;l--){                val++;                a[l][first]=val;            }        }        if(n%2!=0) a[n/2][n/2]=n*n;        return a;    }    }