LeetCode 48. 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]
]
问题解析：
将二维矩阵表示的图片进行旋转。主要是通过旋转前后元素的未知来递推发现规律。
思路1：
最直观的解法，记录原始元素的下标，记录旋转之后的下标，发现元素下标的对应关系为i,j->j,n-i-1。
如果直接原地旋转交换，则会存在问题是遍历下一个的时候，可能已经变成最新的元素了，则又把它变走了。
可以采用额外的矩阵空间来做暂存，但是这样情况 下不满足题目要求。
思路2：
先沿着副对角线旋转，然后再沿着水平中线上下反转即可。
[cc lang=”C++”]
class Solution {
public:
void rotate(vector
const int n = matrix.size();
for(int i=0; i < n; ++i)//沿着副对角线旋转
{
for(int j=0; j
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