【LeetCode 48】Rotate Image 旋转图像

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[LeetCode 48]Rotate Image 旋转图像

Problem description:

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:

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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:

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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]
]

问题描述:

给定一个 n × n 的二维矩阵表示一个图像。

将图像顺时针旋转 90 度。

说明:

你必须在原地旋转图像，这意味着你需要直接修改输入的二维矩阵。请不要使用另一个矩阵来旋转图像。

示例1:

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给定 matrix =
[
  [1,2,3],
  [4,5,6],
  [7,8,9]
],

原地旋转输入矩阵，使其变为:
[
  [7,4,1],
  [8,5,2],
  [9,6,3]
]

示例2:

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给定 matrix =
[
  [ 5, 1, 9,11],
  [ 2, 4, 8,10],
  [13, 3, 6, 7],
  [15,14,12,16]
],

原地旋转输入矩阵，使其变为:
[
  [15,13, 2, 5],
  [14, 3, 4, 1],
  [12, 6, 8, 9],
  [16, 7,10,11]
]

Solution:

将矩阵沿着主对角线翻转一次，再沿着对称线旋转一次即可。

Code:

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class Solution {
    public void rotate(int[][] matrix) {
        int n=matrix[0].length;
        int num=1;
        //沿着主对角线翻转
        for(int i=0;i<n;i++){
            for(int j=0;j<num;j++){
                int temp=matrix[i][j];
                matrix[i][j]=matrix[j][i];
                matrix[j][i]=temp;
            }
            num++;
        }
        //沿着对称轴线翻转
        for(int i=0;i<n;i++){
            for(int j=0;j<n/2;j++){
                int temp=matrix[i][j];
                matrix[i][j]=matrix[i][n-j-1];
                matrix[i][n-j-1]=temp;

            }
        }


    }

}
Thanks!