25. Rotate Image.cpp

/*
Rotate Image
============

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.

Example 1:
Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [[7,4,1],[8,5,2],[9,6,3]]

Example 2:
Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]
Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]

Example 3:
Input: matrix = [[1]]
Output: [[1]]

Example 4:
Input: matrix = [[1,2],[3,4]]
Output: [[3,1],[4,2]]

Constraints:
matrix.length == n
matrix[i].length == n
1 <= n <= 20
-1000 <= matrix[i][j] <= 1000
*/

class Solution
{
public:
  void rotate(vector<vector<int>> &matrix)
  {
    for (int i = 0; i < matrix.size(); ++i)
    {
      for (int j = i; j < matrix.size(); ++j)
      {
        swap(matrix[i][j], matrix[j][i]);
      }
    }

    for (int i = 0; i < matrix.size(); ++i)
    {
      for (int j = 0; j < matrix.size() / 2; ++j)
      {
        swap(matrix[i][j], matrix[i][matrix.size() - j - 1]);
      }
    }
  }
};