# Leetcode 48 rotating image

2020-11-09 19:10:55

## LeetCode48 Rotated image

### Title Description

Given a n × n Two dimensional matrix representation of an image .

Rotate image clockwise 90 degree .

Be careful ： Change it in place

### Examples

`````` Given  matrix =
[
[1,2,3],
[4,5,6],
[7,8,9]
],

In situ rotation input matrix , Turn it into :
[
[7,4,1],
[8,5,2],
[9,6,3]
]
``````
`````` Given  matrix =
[
[ 5, 1, 9,11],
[ 2, 4, 8,10],
[13, 3, 6, 7],
[15,14,12,16]
],

In situ rotation input matrix , Turn it into :
[
[15,13, 2, 5],
[14, 3, 4, 1],
[12, 6, 8, 9],
[16, 7,10,11]
]
``````

### Algorithm analysis

• Flip diagonally
• Flip on the center axis
``````1 2 3
4 5 6
7 8 9

====  Diagonals
1 4 7
2 5 8
3 6 9

====  Central axis
7 4 1
8 5 2
9 6 3
``````

\(O(n^{2})\)

### Java Code

``````class Solution {
static void swap(int[][] matrix, int x1, int y1, int x2, int y2){
int t = matrix[x1][y1];
matrix[x1][y1] = matrix[x2][y2];
matrix[x2][y2] = t;
}
public void rotate(int[][] matrix) {
int n = matrix.length;
for(int i = 0; i < n; i++){
for(int j = 0;j<=i;j++){
swap(matrix,i,j,j,i);
}
}

for(int i = 0;i<n;i++){
for(int j = 0;j<n/2;j++){
swap(matrix,i,j,i,n-j-1);
}
}

}
}
``````