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 []count = {1};
        int [][] m = new int[n][n];
        int start = 0;
        while(start<=n/2){
            fill(m,start,count);
            start++;
        }
        return m;
    }
    public void fill(int[][]m,int start,int[]count){
        int end = m.length-start-1;
        //up
        for(int i=start;i<=end;i++){
            m[start][i] = count[0]++;
        }
        //right
        for(int i=start+1;i<=end;i++){
            m[i][end] = count[0]++;
        }
        //down
        for(int i=end-1;i>=start;i--){
            m[end][i] = count[0]++;
        }
        //left
        for(int i=end-1;i>start;i--){
            m[i][start] = count[0]++;
        }
    }
}