2014
11-19

# LeetCode-Rotate Image[数组]

### Rotate Image

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

Rotate the image by 90 degrees (clockwise).

Could you do this in-place?

\begin{center}
\includegraphics[width=200pt]{rotate-image.png}\\
\figcaption{Rotate Image}\label{fig:rotate-image}
\end{center}

// LeetCode, Rotate Image
// 思路 1，时间复杂度O(n^2)，空间复杂度O(1)
class Solution {
public:
void rotate(vector<vector<int>>& matrix) {
const int n = matrix.size();

for (int i = 0; i < n; ++i)  // 沿着副对角线反转
for (int j = 0; j < n - i; ++j)
swap(matrix[i][j], matrix[n - 1 - j][n - 1 - i]);

for (int i = 0; i < n / 2; ++i) // 沿着水平中线反转
for (int j = 0; j < n; ++j)
swap(matrix[i][j], matrix[n - 1 - i][j]);
}
};


// LeetCode, Rotate Image
// 思路 2，时间复杂度O(n^2)，空间复杂度O(1)
class Solution {
public:
void rotate(vector<vector<int>>& matrix) {
const int n = matrix.size();

for (int i = 0; i < n / 2; ++i) // 沿着水平中线反转
for (int j = 0; j < n; ++j)
swap(matrix[i][j], matrix[n - 1 - i][j]);

for (int i = 0; i < n; ++i)  // 沿着主对角线反转
for (int j = i + 1; j < n; ++j)
swap(matrix[i][j], matrix[j][i]);
}
};