# 48. Rotate Image 旋转图像

Medium

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:

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:

Given input matrix =
[
[ 5, 1, 9,11],  i=0,j=1,n=4
[ 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]
]

``````

``````/*
i=0,j=1,n=4时,
[                          [
[ 5, 1, 9,11],             [15,13, 2, 5],
[ 2, 4, 8,10],   ---->     [14, 3, 4, 1],
[13, 3, 6, 7],             [12, 6, 8, 9],
[15,14,12,16]              [16, 7,10,11]
],                         ]
*/
void rotate2(vector<vector<int>> &matrix){
int n = matrix.size();
for (int i = 0; i<n/2; i++) {
for (int j = i; j<n-1-i; j++) {
int tmp = matrix[i][j];
matrix[i][j] = matrix[n-1-j][i];
matrix[n-1-j][i] = matrix[n-1-i][n-1-j];
matrix[n-1-i][n-1-j] = matrix[j][n-1-i];
matrix[j][n-1-i] = tmp;
}
}
}
``````

``````void rotate(vector<vector<int>>& matrix) {
int n = matrix.size();
for (int i=0; i<n; i++) {
for (int j=i+1; j<n; j++) {
swap(matrix[i][j], matrix[j][i]);
}
reverse(matrix[i].begin(), matrix[i].end());
}
}
``````