rotateImage.java

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

Rotate the image by 90 degrees (clockwise).

Note:

You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

Example 1:

Given input matrix = 
[
  [1,2,3],
  [4,5,6],
  [7,8,9]
],

rotate the input matrix in-place such that it becomes:
[
  [7,4,1],
  [8,5,2],
  [9,6,3]
]
Example 2:

Given input matrix =
[
  [ 5, 1, 9,11],
  [ 2, 4, 8,10],
  [13, 3, 6, 7],
  [15,14,12,16]
], 

rotate the input matrix in-place such that it becomes:
[
  [15,13, 2, 5],
  [14, 3, 4, 1],
  [12, 6, 8, 9],
  [16, 7,10,11]
]*/
public class rotateImage {

	public static void main(String[] args) {
		int[][] matrix = new int[][]{
		                              {1,2,3},
		                              {4,5,6},
		                              {7,8,9}
		                            };
		rotate(matrix);
		System.out.println(matrix);
	}
	
	public static void rotate(int[][] matrix) {
		int length = matrix.length;
        for(int i=0; i<length/2; i++){
        	for(int j=0; j<(length + 1)/2; j++){
        		int temp = matrix[i][j];
        		matrix[i][j] = matrix[length-j-1][i];
        		matrix[length-j-1][i] = matrix[length-i-1][length-j-1];
        		matrix[length-i-1][length-j-1] = matrix[j][length-i-1];
        		matrix[j][length-i-1] = temp;
        	}
        }
    }

}