【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 <algorithm>
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<vector<int> > &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(176)  评论(0编辑  收藏  举报