You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise)..

Note:
You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

Example 1:

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Given input matrix = 
[
  [1,2,3],
  [4,5,6],
  [7,8,9]
],

rotate the input matrix in-place such that it becomes:
[
  [7,4,1],
  [8,5,2],
  [9,6,3]
]

Example 2:

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Given input matrix =
[
  [ 5, 1, 9,11],
  [ 2, 4, 8,10],
  [13, 3, 6, 7],
  [15,14,12,16]
], 

rotate the input matrix in-place such that it becomes:
[
  [15,13, 2, 5],
  [14, 3, 4, 1],
  [12, 6, 8, 9],
  [16, 7,10,11]
]
题意

顺时针90度旋转一个矩阵。

答案
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class Solution {
public:
    void rotate(vector<vector<int> > &matrix) {
        int n = matrix.size();
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<n-i;j++)
            {
                
                swap(matrix[i][j],matrix[n-1-j][n-i-1]);
            }
        }
        for(int i=0;i<n/2;i++)
        {
            for(int j=0;j<n;j++)
            {
                swap(matrix[i][j],matrix[n-i-1][j]);
            }
        }
    }
   
};

思路