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Rotate Image
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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?
题意：给定一个 n * n 的二维图像，将该图像顺时针旋转 90 度
思路：
先沿副对角线翻转一次，再沿水平中线翻转一次
复杂度：时间O(n^2)，空间O(1)
void rotate(vector<vector<int> > &matrix){
int n = matrix.size();
//沿副对角线翻转
for(int i = 0; i < n; ++i){
for(int j = 0; j < n - i; ++j){
int i2 = n - 1 - j, j2 = n - 1 - i;
swap(matrix[i][j], matrix[i2][j2]);
}
}
//沿水平中线翻转
for(int i = 0; i < n/2; ++i){
swap(matrix[i], matrix[n - i - 1]);
}
}