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Rotate Image

Problem​

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.

Solution Approach​

Click - to see solution code
class Solution {
   public:
    void rotate(vector<vector<int>>& matrix) {
        int n = matrix.size();
        for (int i = 0; i < n / 2; i++) {
            for (int j = 0; j < n - 2 * i - 1; j++) {
                swap(matrix[i][i + j], matrix[n - i - 1 - j][i]);
                swap(matrix[n - i - 1 - j][i],
                     matrix[n - i - 1][n - i - 1 - j]);
                swap(matrix[n - i - 1][n - i - 1 - j],
                     matrix[i + j][n - i - 1]);
            }
        }
    }
};