LeetCode Rotate Image

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:

Could you do this in-place?

First use a naive solution: create a new 2D matrix and use the following formula to copy the data.

result[j[n - i - 1] = marix[i][j];

public class Solution {    public void rotate(int[][] matrix) {        int[][] result = new int[matrix.length][matrix.length];        for(int i = 0; i < matrix.length; i++){            for(int j = 0; j < matrix[i].length; j++){                result[j][matrix.length - 1 - i] = matrix[i][j];            }        }        for(int i = 0; i < matrix.length; i++){            for(int j = 0; j < matrix.length; j++){                matrix[i][j] = result[i][j];            }        }    }}

Then consider the in-place case.

The formula becomes:

matrix[i][j] = matrix[n - 1 - j][i];

So the code is as follows:

public class Solution {    public void rotate(int[][] matrix) {        int n = matrix.length;        int[][] result = new int[n][n];        for(int i = 0; i < Math.ceil(((double) n) / 2); i++){            for(int j = 0; j < n / 2; j++){                int temp = matrix[i][j];                matrix[i][j] = matrix[n - 1 - j][i];                matrix[n - 1 - j][i] = matrix[n - 1 - i][n - 1 - j];                matrix[n - 1 - i][n - 1 - j] = matrix[j][n - 1 - i];                matrix[j][n - 1 - i] = temp;            }        }            }}