Rotate Image

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

Solutions

🧠 Cpp

#include <cmath>
class Solution
{

/*
Approach:
rotate by layers
first X that Y
XXXX
XYYX
XYYX
XXXX
*/
public:
    void rotate(vector<vector<int>>& matrix)
    {
        int size = matrix.size();

        for(int i = 0; i < ceil(size/2.0); ++i)
            for(int j = i; j < (size-i*2)-1+i; ++j)
            {
                int temp = matrix[i][j];
                matrix[i][j] = matrix[size-1-j][i];
                matrix[size-1-j][i] = matrix[size-1-i][size-1-j];
                matrix[size-1-i][size-1-j] = matrix[j][size-1-i];
                matrix[j][size-1-i] = temp;
            }
    }
};