0048. Rotate Image

48. Rotate Image#

题目 #

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],
[ 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]
]
``````

解题思路 #

• 给出一个二维数组，要求顺时针旋转 90 度。
• 这一题比较简单，按照题意做就可以。这里给出 2 种旋转方法的实现，顺时针旋转和逆时针旋转。
``````
/*
* clockwise rotate 顺时针旋转
* first reverse up to down, then swap the symmetry
* 1 2 3     7 8 9     7 4 1
* 4 5 6  => 4 5 6  => 8 5 2
* 7 8 9     1 2 3     9 6 3
*/
void rotate(vector<vector<int> > &matrix) {
reverse(matrix.begin(), matrix.end());
for (int i = 0; i < matrix.size(); ++i) {
for (int j = i + 1; j < matrix[i].size(); ++j)
swap(matrix[i][j], matrix[j][i]);
}
}

/*
* anticlockwise rotate 逆时针旋转
* first reverse left to right, then swap the symmetry
* 1 2 3     3 2 1     3 6 9
* 4 5 6  => 6 5 4  => 2 5 8
* 7 8 9     9 8 7     1 4 7
*/
void anti_rotate(vector<vector<int> > &matrix) {
for (auto vi : matrix) reverse(vi.begin(), vi.end());
for (int i = 0; i < matrix.size(); ++i) {
for (int j = i + 1; j < matrix[i].size(); ++j)
swap(matrix[i][j], matrix[j][i]);
}
}

``````

代码 #

``````
package leetcode

func rotate(matrix [][]int) {
row := len(matrix)
if row <= 0 {
return
}
column := len(matrix[0])
// rotate by diagonal 对角线变换
for i := 0; i < row; i++ {
for j := i + 1; j < column; j++ {
tmp := matrix[i][j]
matrix[i][j] = matrix[j][i]
matrix[j][i] = tmp
}
}
// rotate by vertical centerline 竖直轴对称翻转
halfColumn := column / 2
for i := 0; i < row; i++ {
for j := 0; j < halfColumn; j++ {
tmp := matrix[i][j]
matrix[i][j] = matrix[i][column-j-1]
matrix[i][column-j-1] = tmp
}
}
}

``````

Sep 6, 2020