Rotate Image

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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?

描述

给出一个 n*n 的整数型数组，要求将其顺时针旋转 90°，要求不能使用额外数组辅助

分析

将一张纸上下翻转，然后按照对角线翻转，即相当于这张纸旋转 90°

代码

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public class Solution {
    public void rotate(int[][] matrix) {

        int n = matrix.length;

        for (int i = 0; i < n / 2; i++) {     // 上下翻转
            for (int j = 0; j < n; j++) {
                int t = matrix[i][j];
                matrix[i][j] = matrix[n - 1 - i][j];
                matrix[n - 1 - i][j] = t;
            }
        }

        for (int i = 0; i < n; i++) {        // 对角线翻转
            for (int j = i + 1; j < n; j++) {
                int t = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = t;
            }
        }
    }
}