LeetCode:Rotate Image

Rotate Image

Total Accepted: 58066  Total Submissions: 172733  Difficulty: Medium

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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思路：

可以自己拿张方形的纸试一下：

1.先将纸沿副对角线（右上到左下）对折；

2.再将纸沿中心横线对折，即为纸顺时针旋转90度后的结果。

code:

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;j++) {
            if(i+j <n) {
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[n-j-1][n-i-1];
                matrix[n-j-1][n-i-1] = tmp;
            }
        }
        for(int i=0;i<n/2;i++)
        for(int j=0;j<n;j++) {
            int tmp = matrix[i][j];
            matrix[i][j] = matrix[n-i-1][j];
            matrix[n-i-1][j] = tmp;
        }
    }
};