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.
Constraints:
- n == matrix.length == matrix[i].length
- 1 <= n <= 20
- -1000 <= matrix[i][j] <= 1000
Examples:
Input: [[1,2,3],[4,5,6],[7,8,9]]
Output: [[7,4,1],[8,5,2],[9,6,3]]
Explanation: The image is rotated by 90 degrees clockwise.
Solutions
Transpose and Reverse
Time: O(n^2)Space: O(1)
The solution first transposes the matrix (i.e., swaps the row and column indices of each element), and then reverses each row to achieve the rotation effect.
function rotate(matrix) {
let n = matrix.length;
for (let i = 0; i < n; i++) {
for (let j = i; j < n; j++) {
[matrix[j][i], matrix[i][j]] = [matrix[i][j], matrix[j][i]];
}
}
for (let i = 0; i < n; i++) {
matrix[i].reverse();
}
}
Follow-up:
How would you rotate the image by 180 degrees or 270 degrees?
