[Algorithm] Leetcode_ 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.

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

Analsysis & Solution

• 시계방향으로 90도 회전시에 갖게되는 행렬을 구하는 문제
• 행=이전 열, 열=행렬사이즈-현재열 위치-1

Code

//https://leetcode.com/explore/interview/card/top-interview-questions-easy/92/array/770/

class Solution {
    public void rotate(int[][] matrix) {

        int size = matrix.length;
        int[][] arr = new int[size][size];
        for (int i = 0; i < size; i++) {
            for (int j = 0; j < size; j++) {
                arr[j][size - i - 1] = matrix[i][j];
            }
        }

        for (int i = 0; i < size; i++) {
            for (int j = 0; j < size; j++) {
                matrix[i][j] = arr[i][j];
            }
        }

    }
}