LeetCode 48. Rotate Image-优快云博客

本文链接：https://blog.youkuaiyun.com/wuqingdeqing/article/details/100192286

本文详细介绍了一种在不使用额外空间的情况下，将二维矩阵顺时针旋转90度的算法实现。通过中心翻转和沿y轴翻转两步操作，实现了矩阵的有效旋转。

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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]
]

此题旋转90度，采用两步走，先中心翻转后据y翻转。Accepted代码如下：

class Solution {
    public void rotate(int[][] matrix) {
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < i; j++) {
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = tmp;
            }
        }
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length / 2; j++) {
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[i][matrix[0].length - 1 - j];
                matrix[i][matrix[0].length - 1 - j] = tmp;
            }
        }
    }
}