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[leetcode] problem 48 – rotate image

admin 11月 13, 2020 0

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

No.1

Given input matrix = 

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

rotate the input matrix in-place such that it becomes:

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

No.2

Given input matrix =

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6
 
[
  [ 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:

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

Code

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public void (int[][] matrix) {
    int n = matrix.length;

    for (int row = 0; row < n - 1; row++) {
        for (int col = 0; col < n - 1 - row; col++) 
            swap(matrix, row, col, n - 1 - col, n - 1 - row);
    }

    for (int i = 0; i < n / 2 ; i++) {
        for (int j = 0; j < n; j++)
            swap(matrix, i, j, n - 1 - i, j);
    }
}

private void swap(int[][] matrix, int x1, int y1, int x2, int y2) {
    int tmp = matrix[x1][y1];
    matrix[x1][y1] = matrix[x2][y2];
    matrix[x2][y2] = tmp;
}
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