leetcode 48. Rotate Image
z
 2018-03-11 17:19:20  

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