# Rotate Image

`Array`

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 imagein-place, which means you have to modify the input 2D matrix directly.DO NOTallocate 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],
[ 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]
]
``````

## Analysis & Solution

### Approach 1

• Reverse Each Row

• Flip Diagonally

``````class Solution {
public void rotate(int[][] matrix) {
// reverse
reverse(matrix);

// flip
flip(matrix);
}
public void swap(int[] num, int i, int j) {
int tmp = num[i];
num[i] = num[j];
num[j] = tmp;
}

public void reverse(int[][] matrix) {
int n = matrix.length;
// reverse each row
for (int[] row: matrix) {
int i = 0, j = n - 1;
while (i < j) {
swap(row, i, j);
i++;
j--;
}
}
}

// flip by diagonal
public void flip(int[][] matrix) {
int n = matrix.length;
for (int i = 0; i < n; i++) {
for (int j = 0; j < n - 1 - i; j++) {
int tmp = matrix[i][j];
matrix[i][j] = matrix[n - 1 - j][n - 1 - i];
matrix[n - 1 - j][n - 1 - i] = tmp;
}
}
}
}
``````

## Reference

https://leetcode.com/problems/rotate-image/solution/