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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?
将每个[i, j]对应旋转对称的四个点的坐标算出来，然后pixel by pixel的旋转。
公式：matrix[i][j] = matrix[n-1-j][i] i 表示从左到右，j 表示从右到左。
注意当n是奇数时，比如5，要转换到第3列/行，因此 j < Math.ceil((double) n / 2)
Java code:
public class Solution { public void rotate(int[][] matrix) { int n = matrix.length; //matrix[i][j] = matrix[n-1-j][i] 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; } } } }
Reference:
1. http://www.programcreek.com/2013/01/leetcode-rotate-image-java/
2. http://www.cnblogs.com/springfor/p/3886487.html
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原文地址：http://www.cnblogs.com/anne-vista/p/4961843.html
