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You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

You have to rotate the image , which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

Example 1:

Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]Output: [[7,4,1],[8,5,2],[9,6,3]]

Example 2:

Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]

Example 3:

Input: matrix = [[1]]Output: [[1]]

Example 4:

Input: matrix = [[1,2],[3,4]]Output: [[3,1],[4,2]]

Constraints:

• matrix.length == n
• matrix[i].length == n
• 1 <= n <= 20
• -1000 <= matrix[i][j] <= 1000

题意：给定一个 n × n 的二维矩阵表示一个图像。将图像顺时针旋转 90 度。

解法1 额外空间

这种做法就不写了。

解法2 常量空间

class Solution {
   public:    void rotate(vector
   
    
     >& matrix) {
           int n = matrix.size();        for (int i = 0; i < n; ++i)             for (int j = 0; j < i; ++j)                swap(matrix[i][j], matrix[j][i]);          for (int i = 0; i < n; ++i)            reverse(matrix[i].begin(), matrix[i].end());    }};
    
   

运行效率如下：

执行用时：4 ms, 在所有 C++ 提交中击败了64.58% 的用户内存消耗：7.1 MB, 在所有 C++ 提交中击败了69.34% 的用户

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