Array - 48. Rotate Image

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]
]

思路：

题目意思是把一个二维矩阵，顺时针旋转90度，可以一层一层的考虑，以[[ 5, 1, 9,11],[ 2, 4, 8,10],[13, 3, 6, 7],[15,14,12,16]]为例，对于最外层，只需要把5,2,13、15,14,12、16, 7,10、11, 9, 1，顺时针移动一下就实现了这一圈的90度旋转。

代码：

go：

func rotate(matrix [][]int)  {
    if matrix == nil || len(matrix) == 0 {
        return
    }
    
    var ( 
        m =  len(matrix)
        top = 0
        left = 0
        bottom = m - 1
        right = m - 1
    )
    
    for top < bottom {
        for j := 0; j < right - left ; j++ {
            temp := matrix[top][left + j]
            
            matrix[top][left + j] = matrix[bottom - j][left]
            
            matrix[bottom - j][left] = matrix[bottom][right - j]
            
            matrix[bottom][right - j] = matrix[top + j][right]
            
            matrix[top + j][right] = temp
        }
        
        top++
        bottom--
        left++
        right--
    }
    
}