Rotate Image

佚名 6年前 (2019-05-10) 随笔 2200人围观抢沙发百度已收录

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

Rotate the image by 90 degrees (clockwise).

Note:

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You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOTallocate 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]
]

　　顺时针旋转90度时，可以把旋转90度所对应的三角形补充为等边三角形，按边旋转，如图

code

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

class Solution
{
public:
    void rotate(vector<vector<int>>& matrix)
    {
        if(matrix.empty())
            return ;

        tranpose(matrix);
        reflect(matrix);
        return ;
    }
private:
    void tranpose(vector<vector<int>> &matrix)
    {
        for(int i=0;i<matrix.size();++i)
        {
            for(int j=0;j<i;++j)
                swap(matrix.at(i).at(j),matrix.at(j).at(i));
        }
        return ;
    }
    void reflect(vector<vector<int>> &matrix)
    {
        for(int row=0;row<matrix.size();++row)
        {
            for(int i=0,j=matrix.at(row).size()-1;i<j;++i,--j)
                swap(matrix.at(row).at(i),matrix.at(row).at(j));
        }
        return ;
    }
};

int main()
{
    vector<vector<int>> arr{{1,2,3},{4,5,6},{7,8,9}};
    Solution s;
    s.rotate(arr);
    for(auto i:arr)
    {
        for(auto j:i)
            cout<<j<<" ";
        cout<<endl;
    }
    return 0;
}