LeetCode-in-All

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

Solution

#include <vector>

class Solution {
public:
    void rotate(std::vector<std::vector<int>>& matrix) {
        int n = matrix.size();
        for (int i = 0; i < n / 2; ++i) {
            for (int j = i; j < n - i - 1; ++j) {
                std::vector<std::vector<int>> pos = {
                    {i, j}, 
                    {j, n - 1 - i}, 
                    {n - 1 - i, n - 1 - j}, 
                    {n - 1 - j, i}
                };
                int t = matrix[pos[0][0]][pos[0][1]];
                for (int k = 1; k < pos.size(); ++k) {
                    int temp = matrix[pos[k][0]][pos[k][1]];
                    matrix[pos[k][0]][pos[k][1]] = t;
                    t = temp;
                }
                matrix[pos[0][0]][pos[0][1]] = t;
            }
        }
    }
};

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