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
- 矩阵旋转 = 对角翻转 + 中轴翻转 (自己举例子,很容易找到规律)
- 要特别注意
与原矩阵的对应关系(i,j
增加往下走,i
增加往右走)j
func rotate(matrix [][]int) {
n := len(matrix)
// 首先沿对角线反转(\)
for i := 0; i < n; i++ {
for j := i + 1; j < n; j++ {
matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
}
}
// 沿纵轴反转
for i := 0; i < n; i++ {
for j := 0; j < n/2; j++ {
matrix[i][j], matrix[i][n-j-1] = matrix[i][n-j-1], matrix[i][j]
}
}
}