Rotate Image -- LeetCode

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?

思路：将这个矩阵沿左对角线(从左上角到右下角)对称变换，再进行左右对称变换。

class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        for (int i = 0, n = matrix.size(); i < n; i++)
            for (int j = i + 1; j < n; j++)
                swap(matrix[i][j], matrix[j][i]);
        for (int i = 0, n = matrix.size(); i < n; i++)
            for (int j = (n - 1) / 2 + 1; j < n; j++)
                swap(matrix[i][j], matrix[i][n - j - 1]);
    }
};