LeetCode 48. Rotate Image C++

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.

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。
说明：
你必须在原地旋转图像，这意味着你需要直接修改输入的二维矩阵。请不要使用另一个矩阵来旋转图像。

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]
]

分析：

矩阵转置 + 翻转每一行，时间复杂度O(n²)，空间复杂度O(1).

C++

class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        int n = matrix.size();
        //矩阵转置
        for(int i = 0; i < matrix.size(); i++){
        	for(int j = i; j < matrix.size(); j++){
        		swap(matrix[i][j] , matrix[j][i]);
			}
		}
		//翻转每一行
        for(int i = 0; i < matrix.size(); i++){
        	for(int j = 0; j < matrix.size() / 2; j++){
        		swap(matrix[i][j] ,matrix[i][n-j-1]);
			}
		}
    }
};