Leetcode 48 Rotate Image

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?

Solution 1: Pay attention to the math, two loops. O(n^2)

 public class Solution {  
   public void rotate(int[][] matrix) {  
     int n=matrix.length;  
     if (n<=1) return;  
     int lo=0, hi=n-1;  
     while (lo<hi) {  
       for (int i=lo; i<hi; i++) {  
         int temp=matrix[lo][i];  
         matrix[lo][i]=matrix[hi+lo-i][lo];  
         matrix[hi+lo-i][lo]=matrix[hi][hi+lo-i];  
         matrix[hi][hi+lo-i]=matrix[i][hi];  
         matrix[i][hi]=temp;  
       }  
       lo++;  
       hi--;  
     }  
   }  
 }