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一天一道LeetCode系列

（一）题目

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?

（二）解题

90度旋转图像，我们不难看出

class Solution {public:    void rotate(vector
   
    
     >& matrix) {        int n = matrix.size()-1;        vector
     
      
       > tmp = matrix;//深拷贝        for(int i = 0 ; i< n+1; i++)        {            for(int j = 0 ; j < n+1 ; j++)            {                matrix[j][n-i] = tmp[i][j];//赋值转换            }        }    }};
      
     
    
   

网上还有一种解法去先转置在对称变换。代码如下：

class Solution {public:    void rotate(vector
   
    
      > &matrix) {        int dim = matrix.size();        int temp = 0;        for (int i = 0; i < dim; ++i) { //先转置            for (int j = i+1; j < dim; ++j) {                temp = matrix[i][j];                matrix[i][j] = matrix[j][i];                matrix[j][i] = temp;            }        }        for (int i = 0; i < dim/2; ++i) { //然后对称变换            for (int j = 0; j < dim; ++j) {                temp = matrix[j][i];                matrix[j][i] = matrix[j][dim - i -1];                matrix[j][dim - i -1] = temp;            }        }    }};
    
   

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