RotateImage.cs

/*
You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).
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.
*/
public class Solution {
    public void Rotate(int[][] matrix) 
    {
        int n = matrix.Length;
        for(int i = 0; i < n; i++)
        {
            for(int j = i; j < n; j++)
            {
                int temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        }
        for(int i = 0; i < n; i++)
        {
            for(int j = 0; j < n/2; j++)
            {
                int temp = matrix[i][j];
                matrix[i][j] = matrix[i][n - j - 1];
                matrix[i][n - j - 1] = temp;
            }
        }       
    }
}