LeetCode演算法題之Rotate Image__演算法

問題描述：
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?
要求不能另開空間，一開始理解錯了，後來畫圖明白了
解題思路：
首先以對角線為軸對稱交換，再以中間列（如果有的話）為軸對稱交換
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class Solution {public:    void rotate(vector<vector<int> > &matrix) {        if (matrix.empty())             return;        int n = matrix.size(), tmp;        for (int i = 0; i < n; ++i) {            for (int j = 0; j < i; ++j) {                tmp = matrix[i][j];                matrix[i][j] = matrix[j][i];                matrix[j][i] = tmp;            }        }        for (int i = 0; i < n/2; ++i) {            for (int j = 0; j < n; ++j) {                tmp = matrix[i][j];                matrix[i][j] = matrix[n-1-i][j];                matrix[n-1-i][j] = tmp;            }        }        return;    }};