[leetcode-in-go] 0048- Rotate Image

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]

]

解題思路

• 矩陣旋轉 = 對角翻轉 + 中軸翻轉 （自己舉例子，很容易找到規律）
• 要特别注意

  i,j

  與原矩陣的對應關系（

  i

  增加往下走，

  j

  增加往右走）

func rotate(matrix [][]int) {
	n := len(matrix)
	// 首先沿對角線反轉（\）
	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]
		}
	}
	// 沿縱軸反轉
	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]
		}
	}
}