LeetCode | Rotate Image

题目

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

这题就是想清楚移动时索引值得变化关系即可。还要注意一轮移动涉及四个元素，因此只要遍历四分之一的矩阵即可。

代码

public class RotateImage {
	public void rotate(int[][] matrix) {
		int N = matrix.length;
		for (int i = 0; i < N / 2; ++i) {
			for (int j = i; j < N - 1 - i; ++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;
			}
		}
	}
}