48

48. Rotate Image (Medium)

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:

Input: matrix = [[1]]
Output: [[1]]

Example 4:

Input: matrix = [[1,2],[3,4]]
Output: [[3,1],[4,2]]

 

Constraints:

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

Related Topics:
Array

Solution 1.

// OJ: https://leetcode.com/problems/rotate-image/
// Author: github.com/lzl124631x
// Time: O(N^2)
// Space: O(1)
class Solution {
public:
    void rotate(vector<vector<int>>& A) {
        int N = A.size();
        for (int i = 0; i < N / 2; ++i) {
            for (int j = i; j < N - i - 1; ++j) {
                int tmp = A[i][j];
                A[i][j] = A[N - j - 1][i];
                A[N - j - 1][i] = A[N - i - 1][N - j - 1];
                A[N - i - 1][N - j - 1] = A[j][N - i - 1];
                A[j][N - i - 1] = tmp;
            }
        }
    }
};