Rotate Image

Description

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]]

Constraints:

• n == matrix.length == matrix[i].length
• 1 <= n <= 20
• -1000 <= matrix[i][j] <= 1000

Code

class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        // diagonal swap
        for(int i = 0; i < matrix.size(); i++) {
            for(int j = i + 1; j < matrix[i].size(); j++) {
                swap(matrix[i][j], matrix[j][i]);
            }
        }
 
        // row reverse
        for(int i = 0; i < matrix.size(); i++) {
            reverse(matrix[i].begin(), matrix[i].end());
        }
    }
};

Source

• Rotate Image - LeetCode