leetcode || 48、Rotate Image

problem：

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?

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  Array

题意：将一个矩阵顺时针旋转90度

thinking：

（1）题目要求原址操作

（2）先将矩阵 转置，再将矩阵沿中间对称左右翻转

code：

class Solution {
public:
    void rotate(vector<vector<int> > &matrix) {
        int dim = matrix.size();
        int temp = 0;
        for (int i = 0; i < dim; ++i) { //转置
            for (int j = i+1; j < dim; ++j) {
                temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        }
        for (int i = 0; i < dim/2; ++i) { //对称变换
            for (int j = 0; j < dim; ++j) {
                temp = matrix[j][i];
                matrix[j][i] = matrix[j][dim - i -1];
                matrix[j][dim - i -1] = temp;
            }
        }
    }
};