48. Rotate Image.cpp

/*

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]
]



Solution one using swap
Solution two is directly cover
*/

class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        int n = matrix.size(), a = 0, b = n - 1;
        while ( a < b )
        {
            for ( int i = 0; i < b - a; ++i )
            {
                swap( matrix[a][a + i], matrix[a + i][b] );
                swap( matrix[a][a + i], matrix[b][b - i] );
                swap( matrix[a][a + i], matrix[b - i][a] );
            }
            ++a; --b;
        }
    }
};

class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        int n = matrix.size();
        for ( int i = 0; i < n / 2; ++i )
        {
            for ( int j = i; j < n - i - 1; ++j )
            {
                int temp = matrix[i][j];
                matrix[i][j] = matrix[n - j - 1][i];
                matrix[n - j - 1][i] = matrix[n - i - 1][n - j - 1];
                matrix[n - i - 1][n - j - 1] = matrix[j][n - i - 1];
                matrix[j][n - i - 1] = temp;
            }
        }
    }
};