问题描述
You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).
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:
Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [[7,4,1],[8,5,2],[9,6,3]]Example 2:
Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]
Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]Example 3:
代码语言：javascript复制Input: matrix = [[1]]
Output: [[1]]Example 4:
代码语言：javascript复制Input: matrix = [[1,2],[3,4]]
Output: [[3,1],[4,2]]Constraints:
matrix.length == nmatrix[i].length == n1 <= n <= 20-1000 <= matrix[i][j] <= 1000
给定一个 n × n 的二维矩阵表示一个图像。
将图像顺时针旋转 90 度。
题解
给定一个方阵，将方阵顺时针旋转90度；而且要求必须原地选择，直接对矩阵内容进行修改，不能使用别的矩阵进行辅助。
通过观察，可以发现，顺时针矩阵旋转可以通过两步完成：
- 上下翻转
- 主对角线翻转。
完整代码：
代码语言：javascript复制class Solution {
public:
void rotate(vector<vector<int>>& matrix) {
if (matrix.size() <= 0) return;
updown(matrix);
diagonal(matrix);
return;
}
void updown(vector<vector<int>>& matrix){
int size = matrix.size(), t = matrix.size() / 2;
for (int i=0; i< t; i){
for (int j=0; j< size; j){
swap(matrix[i][j], matrix[size-1-i][j]);
}
}
}
void diagonal(vector<vector<int>>& matrix){
int size = matrix.size();
for (int i=0; i< size; i){
for (int j=i; j< size; j){
swap(matrix[i][j], matrix[j][i]);
}
}
}
};
