048 Rotate Image.cs

/*
48. Rotate Image
https://leetcode.com/problems/rotate-image/

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 Solution {
    public void Rotate(int[][] mat) {
        int N = mat.GetLength(0);
        int level = (N >> 1);
        int t = 0;
        for(int i = 0;i<level;i++){
            for(int j = i;j<N-i-1;j++){
                t = mat[i][j];
                mat[i][j] = mat[N-1-j][i];
                mat[N-1-j][i] = mat[N-1-i][N-1-j];
                mat[N-1-i][N-1-j] = mat[j][N-1-i];
                mat[j][N-1-i] = t;                
            }
        }
    }
}