48. Rotate Image
题目
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]
]
解析
- 本题带有技巧，如果允许申请空间，可以直接按列取，放入到新空间的一行即可
class Solution_48 {
public:
void rotate(vector<vector<int>>& matrix) {
// 总的位置坐标关系：rotate[j][n-1-i]=a[i][j]
int n = matrix.size();
reverse(matrix.begin(), matrix.end()); //a[n-1-i][j]=a[i][j]
for (int i = 0; i < n;i++)
{
for (int j = i + 1; j < n;j++)
{
swap(matrix[i][j],matrix[j][i]); // a[i][j]=a[j][i]
}
}
return;
}
};
题目来源
