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?

分析：该题是阿里一道笔试题，要想原地旋转，必须要找到规律，matrix[i][j] 会旋转到matrix[j][n-i-1]的位置，然后把i变成j，j变成n-i-1，继续循环

class Solution {
public:
    void rotate(vector<vector<int> > &matrix)
    {
    	int n = matrix.size()-1,i,j,k;
    	for(i = 0;i < n;i++)
    	{
    		for(j = i;i+j < n;j++)
    		{
    			int x = i,y = j;//因为后面要变换下标，这里改用其他变量
    			int pre = matrix[x][y];//对于val1 -> val2,记录val1的值
    			int next;//记录val2的值
    			for(k = 0;k < 4;k++)//每次移动4次
    			{
    				next = matrix[y][n-x];
    				matrix[y][n-x] = pre;
    				pre = next;
    				int tmp = x;
    				x = y;
    				y = n - tmp;
    			}
    		}
    	}
    }
};

leetcode 之 Rotate Image