[LeetCode]Rotate Image

题目描述:(链接）

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?

解题思路：

先将矩阵选择180度，然后再将矩阵上下折叠。

class Solution {
public:
    void rotate(vector<vector<int> > &matrix) {
        int temp;
        int len = matrix.size();
        
        // 现将矩阵旋转180°
        for(int i = 0; i < len ; ++i){
            for(int j = 0; j < len; ++j){
                if(i + j <= len - 1){
                    temp = matrix[i][j];
                    matrix[i][j] = matrix[len - j - 1][len - i - 1];
                    matrix[len - j - 1][len - i - 1] = temp;
                }
            }
        }
        
        // 将矩阵上下反转
        for(int i = 0; i < len / 2; ++i){
            for(int j = 0; j < len; ++j){
                temp = matrix[i][j];
                matrix[i][j] = matrix[len - 1 - i][j];
                matrix[len - 1 - i][j] = temp;
            }
        }
        
    }
};