[LeetCode] 48. Rotate Image

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.
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]
]

Thought process:
Iterate the matrix from the outer-most layer to the inner most layer. Rotate the layers one by one.

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

Solution (Java):
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class Solution {
    public void rotate(int[][] matrix) {
        for (int i = 0; i < matrix.length / 2; i++) {
            for (int j = i; j < matrix.length - i - 1; j++) {
                rotate(matrix, i, j);
            }
        }
    }
    
    private void rotate(int[][] matrix, int i, int j) {
        int n = matrix.length;
        int temp = matrix[i][j];
        matrix[i][j] = matrix[n - 1 - j][i];
        matrix[n - 1 - j][i] = matrix[n - 1 - i][n - 1 - j];
        matrix[n - 1 - i][n - 1 - j] = matrix[j][n - 1 - i];
        matrix[j][n - 1 - i] = temp;
    }
}

Time complexity: O(n^2), where n is the length of the matrix.
Location: Philadelphia, PA, USA

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