Leetcode: 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

This problem logic is easy, we have only to be careful with the position index.  For instance,

1     2     3     4

5     6     7     8

9   10    11   12

13   14   15   16

We have marked in pink the elements that rotate for row 0, column 1.

public class Solution {
    public void rotate(int[][] matrix) {
        for(int i=0; i<matrix.length/2; i++)
        {
            for (int j=i; j<(matrix.length-1-i); j++)
            {
                int temp = matrix[i][j];
                matrix[i][j]=matrix[matrix.length-1-j][i];
                matrix[matrix.length-1-j][i]= matrix[matrix.length-i-1][matrix.length-j-1];
                matrix[matrix.length-i-1][matrix.length-j-1] = matrix[j][matrix.length-i-1];
                matrix[j][matrix.length-i-1] = temp;
            }
        }
    }
}