Rotate Image (Java)

	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?
	Common question in interview, pay attention to index
	public class Solution {
	public void rotate(int[][] matrix) {
	if( matrix==null ||matrix.length==0){
	return;
	}
	int layer=matrix.length/2;
	for (int l=0; l<layer; l++){
	int st=l;
	int ed=matrix.length-l-1;
	for (int i=st; i<ed; i++){
	// pay attention here, the offset is distance from i to st
	// so because of symmetry reason, we should calculate the distance from ed
	// which is ed-offset
	int offset=i-st;
	int top=matrix[st][i];
	// left to top
	matrix[st][i]=matrix[ed-offset][st];
	// bottom to left
	matrix[ed-offset][st]=matrix[ed][ed-offset];
	// right to bottom
	matrix[ed][ed-offset]=matrix[i][ed];
	// top to right
	matrix[i][ed]=top;
	}
	}
	}
	}

view raw Rotate Image.java hosted with ❤ by GitHub