Leetcode 48: rotate image

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?

对一个n*n的matrix顺时针旋转90,

step1：switch colums with rows

step2：switch columns

class Solution {
//step1: switch columns to rows
//step2: switch columns
public:
    void rotate(vector<vector<int>>& matrix) {
        //sanity check
        if (matrix.size() <= 1) return;
        //step1: switch columns with rows
        for (int i = 0; i < matrix.size(); i++) {
            for (int j = i+1; j < matrix[0].size(); j++) {
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = tmp;
            }
        }
        //step2: switch columns
        for (int left = 0, right = matrix.size()-1; left < right; left++, right--) {
            for (int i = 0; i < matrix.size(); i++) {
                int tmp = matrix[i][left];
                matrix[i][left] = matrix[i][right];
                matrix[i][right] = tmp;
            }
        }
        return;
    }
};