gistfile1.java

class Solution{
	  /*
	  * Space: O(1); Time: O(n^2).
	  */
	  public static int[][] rotate(int[][] image){
	    if(image == null) return image;
	    
	    int n = image[0].length;
	    
	    if(n != image.length) return image;
	    
	    int layer = 0; // Rotation layer.
	    int temp; 
	    
	    for(;layer< n/2; layer++)
	      for(int i = layer; i< n - layer - 1; i++){ // Swap the sides of current layer element by element.
	        temp = image[layer][i];
	        image[layer][i] = image[n-layer-i-1][layer];
	        image[n-layer-i-1][layer] = image[n-layer-1][n-layer-i-1];
	        image[n-layer-1][n-layer-i-1] = image[i][n-layer-1];
	        image[i][n-layer-1] = temp;

	      }
	    return image;
	  }
}