[PS] Leet | 48. 이미지 회전

문제

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.

예시

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]]

조건

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

답

1. [i, i] 대각선을 기준으로 행렬을 뒤집은 후

 

2. 각 행을 수평으로 뒤집으면,

 

오른쪽 90도 회전이 수행됩니다.

/**
 * @param {number[][]} matrix
 * @return {void} Do not return anything, modify matrix in-place instead.
 */
var rotate = function(matrix) {
    let n = matrix.length;

    for (let i=0; i<n; ++i) {
        for (let j=i+1; j<n; ++j) {
            [matrix[i][j], matrix[j][i]] = [matrix[j][i], matrix[i][j]];
        }
    }

    for (let i=0; i<n; ++i) {
        matrix[i].reverse();
    }
};

시간 복잡도 : O(n^2)

공간 복잡도 : O(1)