LeetCode - Rotate Image

Rotate Image

2013.12.15 21:40

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?

Solution:

　　Rotate an nXn 2D matrix in-place. See the picture below and that's how I did the rotation:

　　　　ABCDA

　　　　DEFEB

　　　　CFXFC

　　　　BEFED

　　　　ADCBA

　　Time complexity is O(n^2), space complexity is O(1).

Accepted code:

 1 // 1AC, yes!!!

 2 class Solution {

 3 public:

 4     void rotate(vector<vector<int> > &matrix) {

 5         // IMPORTANT: Please reset any member data you declared, as

 6         // the same Solution instance will be reused for each test case.

 7         int n;

 8         

 9         n = matrix.size();

10         

11         if(n <= 0){

12             return;

13         }

14         

15         int i, j, tmp;

16         int leni = n / 2;

17         int lenj = n - leni;

18         

19         for(i = 0; i < leni; ++i){

20             for(j = 0; j < lenj; ++j){

21                 // extra O(1)

22                 tmp = matrix[i][j];

23                 matrix[i][j] = matrix[n - 1 - j][i];

24                 matrix[n - 1 - j][i] = matrix[n - 1 - i][n - 1 - j];

25                 matrix[n - 1 - i][n - 1 - j] = matrix[j][n - 1 - i];

26                 matrix[j][n - 1 - i] = tmp;

27             }

28         }

29     }

30 };