[leetcode_48]Rotate Image

将一个n*n的矩阵顺时针旋转90度，额外地，能不能原地旋转，就是不开辟额外的空间。
一次AC, 每个位置上的旋转只会影响4个位置上的数组，开一个tmp，搞定。
附上代码：

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class Solution {
public:
    void MoveStep(vector<vector<int>> &matrix,int i,int j,int n)
    {
        int x1 = i;
        int y1 = j;
    
        int x2 = y1;
        int y2 = n - x1;

        int x3 = n - x1;
        int y3 = n - y1;

        int x4 = n - y1;
        int y4 = x1;

        int tmp = matrix[x4][y4];
        matrix[x4][y4] = matrix[x3][y3];
        matrix[x3][y3] = matrix[x2][y2];
        matrix[x2][y2] = matrix[x1][y1];
        matrix[x1][y1] = tmp;
    }
    
    void rotate(vector<vector<int>> &matrix) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        int length = matrix.size();
        int n = length / 2;
        if(length % 2 == 0)
        {
            for(int i = 0; i < n; i++)
            {
                for(int j = 0; j < n; j++)
                {
                    MoveStep(matrix, i, j, length-1);
                }
            }
        }
        else
        {
            for(int i = 0; i < n; i++)
            {
                for(int j = 0; j <= n; j++)
                {
                    MoveStep(matrix, i, j, length-1);
                }
            }
        }
    }
};