48. 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?

by using simple example find the rotate index corresponding to 4 location.

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] <--- matrix[i][j];

Then writing the code is easier.

public class Solution {
    public void rotate(int[][] matrix) {
        if(matrix == null || matrix.length == 1) return;
        int n = matrix.length;
        for(int i=0; i<= n/2; i++){
            for(int j = i; j< n-1-i; j++){
                int tmp = 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] = tmp;
            }
        }

    }
}