Leetcode 细节实现 Rotate Image

本文为senlie原创，转载请保留此地址：http://blog.csdn.net/zhengsenlie

Rotate Image

Total Accepted: 15609 Total
Submissions: 49679My Submissions

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]);
	}
}