【LeetCode & 剑指offer刷题】数组题21：Rotate Image

【LeetCode & 剑指offer刷题】数组题21：Rotate Image

【LeetCode & 剑指offer 刷题笔记】目录（持续更新中...）

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]

]

---

C++

 

//问题：旋转图像（要求：原地顺时针旋转90°）

/*

 * 顺时针旋转方法：先上下翻转，再沿对角线翻转

 * clockwise rotate

 * first reverse up to down, then swap the symmetry

 * 1 2 3     7 8 9     7 4 1

 * 4 5 6  => 4 5 6  => 8 5 2

 * 7 8 9     1 2 3     9 6 3

*/

#include

class Solution

{

public :

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

    {

        reverse ( matrix . begin (), matrix . end ()); //stl中函数,对每列reverse,直接reverse matrix即可

        for ( int i = 0 ; i < matrix . size (); i ++)

        {

            for ( int j = i + 1 ; j < matrix [ i ]. size (); j ++) //注意这里j从i+1开始，因为只需对一半元素执行操作，i=0,j=1~n-1;i=1,j=2~n-1...

            {

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

            }

        }

    }

};

/*

 *  * 逆时针旋转方法：先左右翻转，再沿对角线翻转

 * anticlockwise rotate

 * first reverse left to right, then swap the symmetry

 * 1 2 3     3 2 1     3 6 9

 * 4 5 6  => 6 5 4  => 2 5 8

 * 7 8 9     9 8 7     1 4 7

*/

/*

void anti_rotate(vector > &matrix) {

    for (auto vi : matrix) reverse(vi.begin(), vi.end()); //对每行reverse,故要遍历matrix，reverse内部容器

    for (int i = 0; i < matrix.size(); ++i) {

        for (int j = i + 1; j < matrix[i].size(); ++j)

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

    }

}

*/

 

 

 

 

 

posted @ 2019-01-05 14:33 wikiwen 阅读( ...) 评论( ...) 编辑 收藏