Description
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
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]
]
Discussion
给定一个方阵，代表了一张图片，要求把该图片顺时针旋转90度。
思路比较简单，如下图所示的1, 4, 16, 13四个数字作一组，2, 8, 15, 9四个数字作一组，依次类推，每组四个数字相互交换位置即可。
算法的时间复杂度为O(n^2)。
C++ Code
class Solution {
public:
void rotate(vector<vector<int>>& matrix) {
int row, col;
int n = matrix.size();
col = n - 1;
for(row = 0; row < n / 2; row ++) {
for(col = row; col < n - 1 - row; col ++) {
swap(matrix[row][col], matrix[col][n - 1 - row]);
swap(matrix[row][col], matrix[n - 1 - row][n - 1 - col]);
swap(matrix[row][col], matrix[n - 1 - col][row]);
}
}
}
};