rotate_image.rs

/// 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.
struct Solution;

impl Solution {
    pub fn rotate(matrix: &mut Vec<Vec<i32>>) {
        let n = matrix.len();
        let m = if n % 2 == 0 { n / 2 } else { (n / 2) + 1 };
        let mut temp;

        for i in 0..m {
            for j in 0..n / 2 {
                let back_i = n - i - 1;
                let back_j = n - j - 1;

                temp = matrix[i][j];
                matrix[i][j] = matrix[back_j][i];
                matrix[back_j][i] = matrix[back_i][back_j];
                matrix[back_i][back_j] = matrix[j][back_i];
                matrix[j][back_i] = temp;
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::Solution;

    #[test]
    fn example_1() {
        let mut matrix = vec![vec![1, 2, 3], vec![4, 5, 6], vec![7, 8, 9]];
        Solution::rotate(&mut matrix);
        assert_eq!(matrix, vec![vec![7, 4, 1], vec![8, 5, 2], vec![9, 6, 3]]);
    }

    #[test]
    fn example_2() {
        let mut matrix = vec![
            vec![5, 1, 9, 11],
            vec![2, 4, 8, 10],
            vec![13, 3, 6, 7],
            vec![15, 14, 12, 16],
        ];
        Solution::rotate(&mut matrix);
        assert_eq!(
            matrix,
            vec![
                vec![15, 13, 2, 5],
                vec![14, 3, 4, 1],
                vec![12, 6, 8, 9],
                vec![16, 7, 10, 11]
            ]
        );
    }

    #[test]
    fn five_by_five() {
        let mut matrix = vec![
            vec![1, 2, 3, 4, 5],
            vec![6, 7, 8, 9, 10],
            vec![11, 12, 13, 14, 15],
            vec![16, 17, 18, 19, 20],
            vec![21, 22, 23, 24, 25],
        ];
        Solution::rotate(&mut matrix);
        assert_eq!(
            matrix,
            vec![
                vec![21, 16, 11, 6, 1],
                vec![22, 17, 12, 7, 2],
                vec![23, 18, 13, 8, 3],
                vec![24, 19, 14, 9, 4],
                vec![25, 20, 15, 10, 5]
            ]
        );
    }
}