48 Rotate Image – Medium

Problem:

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?

Thoughts:

This is only a problem about writing formula.

Solutions:

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

Alternative solution:

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