Leetcode 59 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 1: Simple looping code

 public class Solution {  
   public int[][] generateMatrix(int n) {  
     int[][] matrix=new int[n][n];  
     int lo=0, hi=n-1;  
     int i=1;  
     while (lo<hi) {  
       for (int k=lo; k<hi; k++) matrix[lo][k]=i++;  
       for (int k=lo; k<hi; k++) matrix[k][hi]=i++;  
       for (int k=hi; k>lo; k--) matrix[hi][k]=i++;  
       for (int k=hi; k>lo; k--) matrix[k][lo]=i++;  
       lo++;hi--;  
     }  
     if (lo==hi) matrix[lo][lo]=i++;  
     return matrix;  
   }  
 }