48. Rotate Image

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48. Rotate Image

Description

Difficulty: Medium

Related Topics: Array, Math, Matrix

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:

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Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [[7,4,1],[8,5,2],[9,6,3]]

Example 2:

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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

Hints/Notes

  • 2023/08/08
  • Do the diagonal flip first, then reverse each row
  • Leetcode solution(checked)

Solution

Language: C++

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class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        int m = matrix.size();
        int n = matrix[0].size();
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < i; j++) {
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = tmp;
            }
        }
        for (vector<int>& vec : matrix) {
            reverse(vec.begin(), vec.end());
        }
    }
};