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/**
 * 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?
 */
 
public class Solution {
    public void rotate(int[][] matrix) {
        int n = matrix.length;
        for(int i = 0; i < n / 2; i++){
            int first = i;
            int last = n - i - 1;
            for(int j = first; j < last; j++){
                int offset = j - first;
                int top = matrix[first][j];
                matrix[first][j] = matrix[last - offset][first];
                matrix[last - offset][first] = matrix[last][last - offset];
                matrix[last][last - offset] = matrix[j][last];
                matrix[j][last] = top;
            }
        }
    }
}