面试经典150题——Day36

一、题目

48. Rotate Image

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]]

Constraints:

n == matrix.length == matrix[i].length
1 <= n <= 20
-1000 <= matrix[i][j] <= 1000

二、题解

class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        int n = matrix.size();
        //交换主对角线两侧元素
        for(int i = 0;i < n;i++){
            for(int j = 0;j < i;j++){
                swap(matrix[i][j],matrix[j][i]);
            }
        }
        //交换中轴两侧元素
        for(int i = 0;i < n;i++){
            for(int j = 0;j < n/2;j++){
                swap(matrix[i][j],matrix[i][n-j-1]);
            }
        }
    }
};