48. Rotate Image

最新推荐文章于 2024-01-06 15:21:28 发布

wdlsjdl2

最新推荐文章于 2024-01-06 15:21:28 发布

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本文链接：https://blog.youkuaiyun.com/wdlsjdl2/article/details/51952583

本文介绍了一种将二维矩阵按顺时针方向旋转90度的方法，包括一种非原地旋转的解决方案及一种更高效的原地旋转算法。原地旋转算法通过先进行上下翻转再进行对称交换来实现。

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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?

例如

1	2	3
4	5	6
7	8	9

变成

7	4	1
8	5	2
9	6	3

观察规律，新阵(i,j)=原阵(j,n-1-i)

public class Solution {
  public void rotate(int[][] matrix)
	{
		int row=matrix.length;
		if(row<1)
			return ;
		int[][] arr=new int[row][row];
		
		for(int i=0;i<row;i++)
			System.arraycopy(matrix[i], 0, arr[i], 0, row);
		
		for(int i=0;i<row;i++)
			for(int j=0;j<row;j++)
				matrix[j][row-1-i]=arr[i][j];
	
	}
}

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in-place方法，摘自https://discuss.leetcode.com/topic/6796/a-common-method-to-rotate-the-image

here give a common method to solve the image rotation problems.

/*
 * 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
*/
void rotate(vector<vector<int> > &matrix) {
    reverse(matrix.begin(), matrix.end());
    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]);
    }
}

/*
 * 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());
    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]);
    }
}