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

submission

impl Solution {
    // rotate a NxN matrix is just flip it upside down and tranpose
    pub fn rotate(matrix: &mut Vec<Vec<i32>>) {
        // flip
        matrix.reverse();
        // transpose
        for i in 0..matrix.len() {
            for j in 0..i {
                // a bit hard to use std::mem::swap
                let tmp = matrix[j][i];
                matrix[j][i] = matrix[i][j];
                matrix[i][j] = tmp;
            }
        }
    }
}