[LC] 48. 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]

]

class Solution {

    public void rotate(int[][] matrix) {

        int len = matrix.length;

        // rotate diagnal first

        for (int i = 0; i < len; i++) {

            for (int j = 0; j < i; j++) {

                swap(matrix, i, j, j, i);

            }

        }

        // rotate vertical next

        for (int i = 0; i < len; i++) {

            for (int j = 0; j < len/2; j++) {

                swap(matrix, i, j, i, len - 1 - j);

            }

        }

    }

    private void swap(int[][] matrix, int a, int b, int c, int d) {

        int tmp = matrix[a][b];

        matrix[a][b] = matrix[c][d];

        matrix[c][d] = tmp;

    }

}

巴特西

[LC] 48. Rotate Image

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