LeetCode OJ 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?

找规律：

对于n*n的矩阵，只需变换n*n/4次，每次对四个元素变换，如果是单数则中间的那个元素无需变换。

class Solution {public:    void rotate(vector<vector<int> > &matrix) {        int swapTimes = matrix.size() * matrix[0].size() / 4;        int swapStartI, swapStartJ, nowLineEnd, nowLineStart;        swapStartI = swapStartJ = 0;        nowLineEnd = matrix[0].size() - 1;        nowLineStart = 0;        for (int i = 0; i < swapTimes; i++) {            swapFour(matrix[swapStartI][swapStartJ],                     matrix[swapStartJ][matrix.size() - 1 - swapStartI],                     matrix[matrix.size() - 1 - swapStartI][matrix.size() - 1 - swapStartJ],                     matrix[matrix.size() - 1 - swapStartJ][swapStartI]);  // swap four numbers            swapStartI++;            if (swapStartI == nowLineEnd) {                swapStartI = ++nowLineStart;                nowLineEnd--;                swapStartJ++;            }        }    }    void swapFour(int & a, int & b, int & c, int & d) {        int temp;        //int temp = a, a = b, b = c, c = d, d = temp;  // anticlockwise        temp = d, d = c, c = b, b = a, a = temp;  // clockwise    }};