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题目来源于网址：https://leetcode.com/

48. Rotate Image

Description Submission Solutions

Total Accepted: 101913
Total Submissions: 271175
Difficulty: Medium
Contributors: Admin

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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分析：题目要求对一个n*n的二维矩阵顺时针旋转90度，于是根据旋转变换的规律和中心旋转的对称原则对每一行的数据进行变换。

代码如下：

    void rotate(vector<vector<int>>& matrix) {
	int dim=matrix.size();
        int cnt = dim/2;
        int tmp = 0;
        int ss = dim;
        for( int i=0; i<cnt; ++i) {
            ss = dim -1 -2*i;
            for( int j=i; j<ss+i; ++j) {
                tmp = matrix[j][i];                  
                matrix[j][i]  = matrix[i+ss][j];      
                matrix[i+ss][j] = matrix[dim-j-1][i+ss]; 
                matrix[dim-j-1][i+ss] =  matrix[i][dim-j-1]; 
                matrix[i][dim-j-1] = tmp;            
            }
        }
    }