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

 

n*n矩阵顺时针旋转90度，规律 a[i][j]-->a[j][n-i] 

思路1.按规律逐行拷贝，需要开辟一个新的二维数组，空间复杂度略高

      2.按规律逐个元素和目标位置替换，发现每替换4次，坐标就会回到开始的地方

          以4*4的矩阵为例 a[0][0] --> a[0][3] --> a[3][3] -->a[3][0] --->a[0][0]

          元素4个一组分组，每遍历一行（n-1），最外圈的的元素构成的正方形就已经达成目标了

          缩小正方形逐行替换即可

public class Solution {
        public void rotate(int[][] matrix) {
            if(matrix == null ||matrix.length <= 1){
                return;
            }
            int n = matrix.length;
            int rectangleLen = n;
            int row = 0;
            while(rectangleLen >=2){
                for(int i =row;i<= n-2 - row ;i++){
                    rotateRectangle(matrix,n,row,i);    
                }
                rectangleLen-= 2;
                row ++;
            }
        }
        
        public void rotateRectangle(int[][] matrix,int n,int x_pos,int y_pos){
            int temp = matrix[x_pos][y_pos];
            int target  = 0;
            int temp_pos = 0;
            for(int i=0;i<4;i++){
                target = temp;
                //target position
                temp_pos = x_pos;
                x_pos = y_pos;
                y_pos = n - 1 - temp_pos;
                temp  = matrix[x_pos][y_pos];
                //replace
                matrix[x_pos][y_pos] = target; 
            }
        }
}